Fix handling for compileSdkVersion strings

If compileSdkVersion is a string (as defined in template-params.xml),
the template for build.gradle was failing to properly quote it.

Change-Id: I8ae38213bdb26383982effe2fffcbc2528e3a2bf
diff --git a/templates/base/_MODULE_/build.gradle.ftl b/templates/base/_MODULE_/build.gradle.ftl
index 6d9b5f2..aa5617b 100644
--- a/templates/base/_MODULE_/build.gradle.ftl
+++ b/templates/base/_MODULE_/build.gradle.ftl
@@ -48,8 +48,10 @@
 android {
      <#-- Note that target SDK is hardcoded in this template. We expect all samples
           to always use the most current SDK as their target. -->
-<#if (sample.compileSdkVersion)?is_number || (sample.compileSdkVersion)?is_string>
+<#if (sample.compileSdkVersion)?is_number >
     compileSdkVersion ${sample.compileSdkVersion}
+<#elseif (sample.compileSdkVersion)?is_string>
+    compileSdkVersion "${sample.compileSdkVersion}"
 <#else>
     compileSdkVersion 18
 </#if>