try to fix mac CI

.travis.yml

@@ -9,10 +9,10 @@ jobs:
       language: shell       # 'language: python' is an error on Travis CI macOS, could be generic
 install: 
   - python3 -m pip install --upgrade pip setuptools  
-  - python3 -m pip install --no-use-pep517 --editable .
 # fabio could not be installed as a dependency on mac automatically
   - python3 -m pip install cython
   - python3 -m pip install fabio
+  - python3 -m pip install --no-use-pep517 --editable .  
 # 'python3' is a 'command not found' error on Windows but 'py' works on Windows only
 script: 
   - OMP_NUM_THREADS=2 python3 -m pytest