Merge pull request #404 from radarhere/trusty

Fix failing trusty job

.travis.yml

@@ -15,6 +15,7 @@ matrix:
   include:
     - os: linux
       dist: trusty
+      language: python
     # 64-bit builds
     - os: linux
       dist: xenial

tests/test_supported_wheels.sh

 # Test supported wheels script
 PYTHON_EXE=${PYTHON_EXE:-python}
 if [ -z "$PIP_CMD" ]; then
-    pip_install="$PYTHON_EXE -m pip install --user"
+    pip_install="$PYTHON_EXE -m pip install"
 else
     pip_install="$PIP_CMD install"
 fi