Update sentry-admin.sh to select its own working directory (#3184)

`sentry-admin.sh` only works when called from the working directory and not using its absolute path.

This change makes it also callable using its absolute path.

Author: theoriginalgri

sentry-admin.sh

@@ -1,5 +1,8 @@
 #!/bin/bash
 
+# Set the script directory as working directory.
+cd $(dirname $0)
+
 # Detect docker and platform state.
 source install/dc-detect-version.sh
 source install/detect-platform.sh