add zshrc param to exec

I use appium0.13.0 by CLI and receive the exception of the following

```
"Could not find node using `which node`, at /usr/local/bin/node, at /opt/local/bin/node, at $NODE_BIN, or by querying Appium.app. Where is it
```
https://github.com/appium/appium/blob/master/lib/devices/ios/uiauto/lib/instruments_client_launcher.js#L200

I had set the $NODE_BIN, but it did not load because it did not write only to zshrc.
So I was modified to read the configuration from zshrc