tox: pass TERM

Ref: tox-dev/tox#1441

Author: blueyed

tox.ini

@@ -21,7 +21,7 @@ commands =
     {env:_PYTEST_TOX_COVERAGE_RUN:} pytest {posargs:{env:_PYTEST_TOX_DEFAULT_POSARGS:}}
     coverage: coverage combine
     coverage: coverage report -m
-passenv = USER USERNAME COVERAGE_* TRAVIS PYTEST_ADDOPTS
+passenv = USER USERNAME COVERAGE_* TRAVIS PYTEST_ADDOPTS TERM
 setenv =
     _PYTEST_TOX_DEFAULT_POSARGS={env:_PYTEST_TOX_POSARGS_LSOF:} {env:_PYTEST_TOX_POSARGS_XDIST:}