Do not install test dependencies on CPython dev versions in travis as they are...

Do not install test dependencies on CPython dev versions in travis as they are likely to fail in pre-releases.

.travis.yml

@@ -150,8 +150,8 @@ script:
     else
       STYLE_ARGS=--no-code-style;
       if $PYTHON_DBG -V >&2; then CFLAGS="-O0 -ggdb" $PYTHON_DBG runtests.py -vv --no-code-style Debugger --backends=$BACKEND; fi;
-      if [ -z "${BACKEND##*cpp*}" -a -n "${TRAVIS_PYTHON_VERSION##2.6*}" -a -n "${TRAVIS_PYTHON_VERSION##3.8*}" ]; then pip install pythran; fi;
-      if [ "$BACKEND" != "cpp" -a -n "${TRAVIS_PYTHON_VERSION##2*}" ]; then pip install mypy; fi;
+      if [ -z "${BACKEND##*cpp*}" -a -n "${TRAVIS_PYTHON_VERSION##*-dev}" ]; then pip install pythran; fi;
+      if [ "$BACKEND" != "cpp" -a -n "${TRAVIS_PYTHON_VERSION##2*}" -a -n "${TRAVIS_PYTHON_VERSION##*-dev}" ]; then pip install mypy; fi;
     fi
   - if [ "$COVERAGE" != "1" ]; then CFLAGS="-O2 -ggdb -Wall -Wextra $(python -c 'import sys; print("-fno-strict-aliasing" if sys.version_info[0] == 2 else "")')" python setup.py build_ext -i; fi
   - CFLAGS="-O0 -ggdb -Wall -Wextra" python runtests.py -vv $STYLE_ARGS -x Debugger --backends=$BACKEND $(if [ "$COVERAGE" == "1" ]; then echo " --coverage"; fi) $(if [ -z "$TEST_CODE_STYLE" ]; then echo " -j7 "; fi)