Fix SwiftLint script to execute in correct location via the sample apps

Summary:
Periodically the sample apps build jobs would fail. I discovered this was because SwiftLint wasn't executing out of the current location, and so it was throwing an error when it couldn't find the SwiftLint yml file in the correct relative location.

This diff improves the linting script by making sure all of the relative paths are based off the scripts on-disk location.

Reviewed By: fethica

Differential Revision: D50294909

fbshipit-source-id: 3f5f65e629fe311d1b50d3f86bb458839482f5a1

scripts/lint.sh

@@ -10,6 +10,9 @@ if test -d "/opt/homebrew/bin/"; then
   export PATH
 fi
 
+# Make sure bash executes from the same directory as the script
+cd "$(cd -P -- "$(dirname -- "$0")" && pwd -P)"
+
 VERSION="0.50.3"
 FOUND=$(swiftlint version)