Document the getSourceReport rpc in service.md. Bump version to 3.1.

runtime/observatory/tests/service/get_version_rpc_test.dart

Index: runtime/observatory/tests/service/get_version_rpc_test.dart
diff --git a/runtime/observatory/tests/service/get_version_rpc_test.dart b/runtime/observatory/tests/service/get_version_rpc_test.dart
index 3df8d6788cd636aaa1bdf1c7e33948fe31dc0cec..f72c425aad9b49dc9dd01b3a3e2c09162068e227 100644
--- a/runtime/observatory/tests/service/get_version_rpc_test.dart
+++ b/runtime/observatory/tests/service/get_version_rpc_test.dart
@@ -13,7 +13,7 @@ var tests = [
     var result = await vm.invokeRpcNoUpgrade('getVersion', {});
     expect(result['type'], equals('Version'));
     expect(result['major'], equals(3));
-    expect(result['minor'], equals(0));
+    expect(result['minor'], equals(1));
     expect(result['_privateMajor'], equals(0));
     expect(result['_privateMinor'], equals(0));
   },