Set compile_sdk to '21' instead of 'android-21'

Change-Id: Ia1b24fa2ba29e9040ec97ce9d90fc9fa47f53da2
diff --git a/templates/include/common.ftl b/templates/include/common.ftl
index 281baa7..0808b8c 100644
--- a/templates/include/common.ftl
+++ b/templates/include/common.ftl
@@ -38,7 +38,7 @@
 <#elseif (sample.compileSdkVersion)?has_content>
     <#assign compile_sdk = sample.compileSdkVersion/>
 <#else>
-    <#assign compile_sdk = "\"android-21\""/>
+    <#assign compile_sdk = "21"/>
 </#if>
 <#-- Set the global build tools version -->
 <#assign build_tools_version='"21.0.0"'/>