travis: On fail, cd to tests directory before diffing.

.travis.yml

@@ -16,4 +16,4 @@ script:
   - make -C stmhal
   - cd tests && MICROPY_CPYTHON3=python3.3 ./run-tests
 
-after_failure: for exp in *.exp; do testbase=$(basename $exp .exp); echo -e "\nFAILURE $testbase"; diff $testbase.exp $testbase.out; done
+after_failure: cd tests && for exp in *.exp; do testbase=$(basename $exp .exp); echo -e "\nFAILURE $testbase"; diff $testbase.exp $testbase.out; done