build(aio): upgrade to @angular/material#2.0.0-beta.3 (#15606)

aio/src/styles/main.scss

@@ -1,8 +1,8 @@
 // import global themes
-@import '~@angular/material/core/theming/all-theme';
+@import '~@angular/material/theming';
 @import './ng-io-theme';
 
-// import global variables / 
+// import global variables /
 @import './constants';
 
 // import global mixins

aio/src/styles/ng-io-theme.scss

@@ -1,4 +1,4 @@
-@import '~@angular/material/core/theming/all-theme';
+@import '~@angular/material/theming';
 // Plus imports for other components in your app.
 
 // Include the base styles for Angular Material core. We include this here so that you only