examples: Upgrade Maven plugin versions

Upgrade Maven to 3.8.8, the oldest supported version, as the plugins required a
newer version.

Author: ejona86

buildscripts/grpc-java-artifacts/Dockerfile

@@ -28,6 +28,6 @@ RUN mkdir -p "$ANDROID_HOME/cmdline-tools" && \
     yes | "$ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager" --licenses
 
 # Install Maven
-RUN curl -Ls https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.3.9/apache-maven-3.3.9-bin.tar.gz | \
+RUN curl -Ls https://dlcdn.apache.org/maven/maven-3/3.8.8/binaries/apache-maven-3.8.8-bin.tar.gz | \
     tar xz -C /var/local
-ENV PATH /var/local/apache-maven-3.3.9/bin:$PATH
+ENV PATH /var/local/apache-maven-3.8.8/bin:$PATH

examples/example-debug/pom.xml

@@ -98,7 +98,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/example-dualstack/pom.xml

@@ -102,7 +102,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/example-gauth/pom.xml

@@ -96,7 +96,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/example-hostname/pom.xml

@@ -98,7 +98,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/example-jwt-auth/pom.xml

@@ -94,7 +94,7 @@
       <plugin>
         <groupId>org.xolstice.maven.plugins</groupId>
         <artifactId>protobuf-maven-plugin</artifactId>
-        <version>0.5.1</version>
+        <version>0.6.1</version>
         <configuration>
           <protocArtifact>
             com.google.protobuf:protoc:${protoc.version}:exe:${os.detected.classifier}
@@ -116,7 +116,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/example-oauth/pom.xml

@@ -99,7 +99,7 @@
       <plugin>
         <groupId>org.xolstice.maven.plugins</groupId>
         <artifactId>protobuf-maven-plugin</artifactId>
-        <version>0.5.1</version>
+        <version>0.6.1</version>
         <configuration>
           <protocArtifact>
             com.google.protobuf:protoc:${protoc.version}:exe:${os.detected.classifier}
@@ -121,7 +121,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/example-tls/pom.xml

@@ -82,7 +82,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>

examples/pom.xml

@@ -110,7 +110,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-enforcer-plugin</artifactId>
-        <version>1.4.1</version>
+        <version>3.5.0</version>
         <executions>
           <execution>
             <id>enforce</id>