Fix to readme.

Author: philip-alldredge

README.md

@@ -183,7 +183,7 @@ required = false
 # See https://developer.android.com/guide/topics/manifest/uses-permission-element
 [[package.metadata.android.permission]]
 name = "android.permission.WRITE_EXTERNAL_STORAGE"
-maxSdkVersion = "18"
+max_sdk_version = "18"
 
 [[package.metadata.android.permission]]
 name = "android.permission.CAMERA"