chore(button-toggle): add mat- prefix (#2826)

src/lib/button-toggle/button-toggle.ts

@@ -280,7 +280,7 @@ export class MdButtonToggleGroupMultiple {
 /** Single button inside of a toggle group. */
 @Component({
   moduleId: module.id,
-  selector: 'md-button-toggle',
+  selector: 'md-button-toggle, mat-button-toggle',
   templateUrl: 'button-toggle.html',
   styleUrls: ['button-toggle.css'],
   encapsulation: ViewEncapsulation.None,

src/lib/core/compatibility/compatibility.ts

@@ -26,6 +26,7 @@ export const MAT_ELEMENTS_SELECTOR = `
   [mat-tab-nav-bar],
   mat-autocomplete,
   mat-button-toggle-group,
+  mat-button-toggle,
   mat-card,
   mat-card-actions,
   mat-card-content,
@@ -83,6 +84,7 @@ export const MD_ELEMENTS_SELECTOR = `
   [md-tab-nav-bar],
   md-autocomplete,
   md-button-toggle-group,
+  md-button-toggle,
   md-card,
   md-card-actions,
   md-card-content,