add cronet proguard rule to release buildType

app/build.gradle

@@ -81,7 +81,7 @@ android {
 
             minifyEnabled true
             shrinkResources true
-            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro', 'cronet-proguard-rules.pro'
         }
         debug {
             if (project.hasProperty("RELEASE_STORE_FILE")) {