Update .gitlab-ci.yml

1 job for python2.7 in 3 minutes and 19 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #3155
build_image

00:03:19

 
Name Stage Failure
failed
build_image Build
-- Configuring incomplete, errors occurred!
See also "/home/install/corpus2mwe/build/CMakeFiles/CMakeOutput.log".
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
PYTHON_LIBRARY (ADVANCED)
linked by target "_corpus2mwe" in directory /home/install/corpus2mwe/swig

The command '/bin/sh -c mkdir corpus2mwe/build && cd corpus2mwe/build && cmake .. && cmake --build . && cpack' returned a non-zero code: 1
ERROR: Job failed: exit code 1