fix unexpected char: '\' error on windows

error occurred when register additional directory for android module on windows.

### config.py ###
```
def can_build(plat):
 return plat=="android"

def configure(env):
 if (env['platform'] == 'android'):
  env.android_add_res_dir("android/res")
```

platform/android/SCsub

@@ -65,17 +65,17 @@ for x in env.android_java_dirs:
 gradle_res_dirs_text=""
 
 for x in env.android_res_dirs:
-	gradle_res_dirs_text+=",'"+x+"'"
+	gradle_res_dirs_text+=",'"+x.replace("\\","/")+"'"
 
 gradle_aidl_dirs_text=""
 
 for x in env.android_aidl_dirs:
-	gradle_aidl_dirs_text+=",'"+x+"'"
+	gradle_aidl_dirs_text+=",'"+x.replace("\\","/")+"'"
 
 gradle_jni_dirs_text=""
 
 for x in env.android_jni_dirs:
-	gradle_jni_dirs_text+=",'"+x+"'"
+	gradle_jni_dirs_text+=",'"+x.replace("\\","/")+"'"
 
 gradle_asset_dirs_text=""