remove pushd and popd from travis

[ianhi]

In cytoscape/ipycytoscape#124 (relevant commit) I found that these lines

widget-ts-cookiecutter/{{cookiecutter.github_project_name}}/.travis.yml

Lines 58 to 60 in 0e4a4cd

	pushd $(mktemp -d)
	py.test -l --cov-report xml:$TRAVIS_BUILD_DIR/coverage.xml --cov={{ cookiecutter.python_package_name }} --pyargs {{ cookiecutter.python_package_name }} || EXIT_STATUS=$?
	popd

prevented the nbval tests from running the examples. Changing it to:

       pytest -l --cov-report xml:$TRAVIS_BUILD_DIR/coverage.xml --cov={{ cookiecutter.python_package_name }} || EXIT_STATUS=$? 

got the nbval tests to run again. Though I'm not sure if this was the correct approach because I don't know what the consequences of removing pushd and popd are.

If this was a reasonable change I can make a PR changing the cookiecutter.

[jtpio]

Fixed by #91 which removed Travis