Gradle Build: Exclude additional files

Removing below files from sample code emitGradle output,
since they aren't relevant for users.

Files:
- .gradle
- _index.jd
- buildSrc
- proguard-project.xml

Change-Id: Ie98f36964a2dd044c467959e0e9b8f037bb4728e
diff --git a/build.gradle b/build.gradle
index d74ccb0..db5ca15 100644
--- a/build.gradle
+++ b/build.gradle
@@ -126,7 +126,11 @@
     into outputPath
     from("${inputPath}") {
         // Paths to exclude from output
+        exclude ".gradle"
+        exclude "_index.jd"
         exclude "buildSrc"
+        exclude "template-params.xml"
+        exclude "**/proguard-project.txt"
     }
     // Remove BEGIN_EXCLUDE/END_EXCLUDE blocks from source files
     eachFile { file ->