Fixed wrong Android React Native path. (#3180)

docs/docs/Installing.md

 			jcenter()
 			maven {
 	           // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
-	           url "$rootDir/../../node_modules/react-native/android"
+	           url "$rootDir/../node_modules/react-native/android"
 			}
 		}
 	}