Pin stubs to 7.5.1

Author: adam-urbanczyk

.travis.yml

@@ -58,7 +58,7 @@ before_install:
 - conda env create -f environment.yml
 - source ~/miniconda/bin/activate cadquery
 - conda install -c conda-forge -c defaults -c cadquery python=$PYTHON_VERSION mypy
-- pip install git+https://github.com/CadQuery/OCP-stubs.git
+- pip install git+https://github.com/CadQuery/OCP-stubs.git@7.5.1
 
 install:
 - python setup.py install