docs (md elevation guide): $s removed from code.

Author: M-a-c

guides/mat-elevation.md

@@ -21,10 +21,10 @@ $zValue must be a value between 0 and 24, inclusive.
 How to use the mixin 
 ```scss
 .myClass {
-  @include $mat-elevation(2);
+  @include mat-elevation(2);
 
   &:active {
-    @include $mat-elevation(8);
+    @include mat-elevation(8);
   }
 }
 ```

src/examples/elevation-overview/elevation-overview-example.scss

@@ -11,10 +11,11 @@ div {
     margin-top: 10px;
 }
 
+
 .dynamimc {
-    @include $mat-elevation(2);
+    @include mat-elevation(2);
 
     &:active {
-        @include $mat-elevation(8);
+        @include mat-elevation(8);
     }
 }