fix(readability): changed text opacity from .54 to .87 according the spec (#91)

Author: EladBezalel

material.angular.io/src/app/pages/component-viewer/_component-viewer-theme.scss

@@ -8,10 +8,10 @@
   $foreground: map-get($theme, foreground);
 
   app-component-viewer {
-    color: mat-color($foreground, secondary-text);
+    color: mat-color($foreground, text);
 
     .mat-tab-label:focus {
-      color: mat-color($foreground, secondary-text);
+      color: mat-color($foreground, text);
     }
 
   }

material.angular.io/src/styles/_typography-theme.scss

@@ -11,11 +11,11 @@
   .docs-guide-content {
        h1 {
         color: mat-color($primary, 800);
-        background: rgba(mat-color($foreground, secondary-text), .03);
+        background: rgba(mat-color($foreground, text), .03);
       }
 
       h3, h2, h4, h5, p, ol, li{
-        color: mat-color($foreground, secondary-text);
+        color: mat-color($foreground, text);
       }
 
       a {
@@ -27,16 +27,16 @@
       }
 
       table tbody th{
-        border: 1px solid rgba(mat-color($foreground, secondary-text), .03);
+        border: 1px solid rgba(mat-color($foreground, text), .03);
       }
 
       td {
-        color: mat-color($foreground, secondary-text);
+        color: mat-color($foreground, text);
         border: 1px solid rgba(mat-color($foreground, secondary-text), .03);
       }
 
       th {
-        color: mat-color($foreground, secondary-text);
+        color: mat-color($foreground, text);
         background: rgba(mat-color($foreground, secondary-text), .03);
       }
   }