Bug in syntax for old scipy version

Author: rtavenar

.travis.yml

@@ -27,7 +27,7 @@ before_script: # configure a headless display to test plot generation
 install:
   - pip install -r requirements.txt
   - pip install numpy>=1.14  # for numpy array formatting in doctests
-  - pip install scipy<1.3  # otherwise, pymanopt fails, cf <https://github.com/pymanopt/pymanopt/issues/77>
+  - pip install "scipy<1.3"  # otherwise, pymanopt fails, cf <https://github.com/pymanopt/pymanopt/issues/77>
   - pip install flake8 pytest "pytest-cov<2.6"
   - pip install .
 # command to run tests + check syntax style