Bug: python binding fails to be built on Linux

[yuki-koyama]

Travis CI fails to build the python binding on Linux.

https://travis-ci.com/yuki-koyama/sequential-line-search/jobs/184545826

Error messages:

$ cmake -DSEQUENTIAL_LINE_SEARCH_BUILD_COMMAND_DEMOS=OFF -DSEQUENTIAL_LINE_SEARCH_BUILD_VISUAL_DEMOS=OFF -DSEQUENTIAL_LINE_SEARCH_BUILD_PHOTO_DEMOS=OFF -DSEQUENTIAL_LINE_SEARCH_BUILD_PYTHON_BINDING=ON . && make
-- NLopt version 2.5.0
-- Found PythonInterp: /opt/pyenv/shims/python3.7 (found version "1.4") 
CMake Error at external/pybind11/tools/FindPythonLibsNew.cmake:95 (message):
  Python config failure:
  pyenv: python3.7: command not found
  
  The `python3.7' command exists in these Python versions:
    3.7
    3.7.1
  
Call Stack (most recent call first):
  external/pybind11/tools/pybind11Tools.cmake:16 (find_package)
  external/pybind11/CMakeLists.txt:33 (include)
-- Configuring incomplete, errors occurred!
See also "/home/travis/build/yuki-koyama/sequential-line-search/CMakeFiles/CMakeOutput.log".
See also "/home/travis/build/yuki-koyama/sequential-line-search/CMakeFiles/CMakeError.log".

[yuki-koyama]

This issue was solved by #22