Use pip install --user

.travis.yml

@@ -380,7 +380,7 @@ matrix:
     - os: linux
       env: CMAKE_INSTALL_TEST=1
       script:
-        - pip install cmake
+        - pip install --user cmake
         - mkdir __build__ && cd __build__
         - cmake -DBOOST_ENABLE_CMAKE=1 -DBoost_VERBOSE=1 -DBOOST_INCLUDE_LIBRARIES=endian -DCMAKE_INSTALL_PREFIX=~/.local ..
         - cmake --build . --target install