fix(android): add missing namespace to support AGP 7.0+ (#143)

Author: yen-kadokawa

rollbar_flutter/android/build.gradle

@@ -33,6 +33,7 @@ apply plugin: 'checkstyle'
 apply plugin: "com.github.spotbugs"
 
 android {
+    namespace 'com.rollbar.flutter'
     compileSdkVersion 31
 
     compileOptions {