[tooling] Use PYTHONPATH in test download script (#223)

# Exercise Review

## Exercise Discussion

Fixes #222 

## Checklist

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not currently in review?
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Author: jovnc

test-download.sh

@@ -1,3 +1,4 @@
 #!/bin/bash
 
-python scripts/test-download.py $1
+# PYTHONPATH tells python to look for modules in the current directory
+PYTHONPATH="." python scripts/test-download.py $1