Change packager project root path so RNTester can start

Summary:
A quick fix to ensure RNTest works. This PR changes the process root for where packager is run, resulting in the right `cwd` directory path when RN launches RNTester.
Closes https://github.com/facebook/react-native/pull/13947

Differential Revision: D5052093

Pulled By: davidaurelio

fbshipit-source-id: 506a8cd63f1709c948bcc4586467020d380ba85e

packager/launchPackager.command

@@ -12,8 +12,8 @@ echo -en "\033]0;React Packager\a"
 clear
 
 THIS_DIR=$(dirname "$0")
-pushd "$THIS_DIR"
+pushd "$THIS_DIR/.."
-source ./packager.sh
+source packager/packager.sh
 popd
 
 echo "Process terminated. Press <enter> to close the window"