customize the generate sourcemap file or not (#381)

Author: pengcao1

README.md

@@ -189,6 +189,13 @@ For your app crashes to show up with a fully symbolicated stack trace, we will a
 
 If your app token is defined as a constant, you can set an environment variable `INSTABUG_APP_TOKEN` to be used instead.
 
+To disable the automatic upload in android, you can set the following property your build.gradle:
+```dart
+ext {
+    instabugUploadEnable = false;
+}
+```
+
 ## Network Logging
 
 Instabug network logging is enabled by default. It intercepts any requests performed with `fetch` or `XMLHttpRequest` and attaches them to the report that will be sent to the dashboard. To disable network logs:

android/build.gradle

@@ -50,7 +50,8 @@ task upload_sourcemap(type: Exec) {
 }
 
 tasks.whenTaskAdded { task ->
-    if (task.name == 'preReleaseBuild') {
+    if (task.name == 'preReleaseBuild' &&
+        rootProject.hasProperty("instabugUploadEnable") ? rootProject.instabugUploadEnable : true) {
         task.dependsOn upload_sourcemap 
     }
 }