Bump prospector from 1.2.0 to 1.3.1

Bumps [prospector](https://github.com/PyCQA/prospector) from 1.2.0 to 1.3.1.
- [Release notes](https://github.com/PyCQA/prospector/releases)
- [Changelog](https://github.com/PyCQA/prospector/blob/master/CHANGELOG.rst)
- [Commits](prospector-dev/prospector@1.2.0...1.3.1)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

build/test-requirements.txt

@@ -7,7 +7,7 @@ black ; python_version>='3.6'
 yapf
 pylint
 pycodestyle
-prospector==1.2.0 # Last version of prospector with Python 2.7 support
+prospector==1.3.1 # Last version of prospector with Python 2.7 support
 pydocstyle
 nose
 pytest==4.6.9 # Last version of pytest with Python 2.7 support