fix: sort links alphabetically (#996)

Author: crisbeto

material.angular.io/src/app/shared/documentation-items/documentation-items.ts

@@ -129,6 +129,15 @@ const DOCS: { [key: string]: DocItem[] } = {
       },
       additionalApiDocs: [{name: 'Testing', path: 'material-chips-testing.html'}],
     },
+    {
+      id: 'core',
+      name: 'Core',
+      summary: 'Reusable parts used by other components in the library.',
+      exampleSpecs: {
+        prefix: 'core-',
+      },
+      additionalApiDocs: [{name: 'Testing', path: 'material-core-testing.html'}],
+    },
     {
       id: 'datepicker',
       name: 'Datepicker',
@@ -372,15 +381,6 @@ const DOCS: { [key: string]: DocItem[] } = {
         prefix: 'tree-',
       },
     },
-    {
-      id: 'core',
-      name: 'Core',
-      summary: 'Reusable parts used by other components in the library.',
-      exampleSpecs: {
-        prefix: 'core-',
-      },
-      additionalApiDocs: [{name: 'Testing', path: 'material-core-testing.html'}],
-    },
   ],
   [CDK]: [
     {