Clean up build matrix

.travis.yml

@@ -1,18 +1,19 @@
 language: julia
 julia:
     - 1
-env:
-    - PY=python3
-    - PATH=$HOME/.local/bin:$PATH
 
 jobs:
   include:
     - name: "Linux"
       os: linux
       before_install: sudo apt-get -y install python3-pip python3-setuptools
+      env:
+        - PY=python3 PATH=$HOME/.local/bin:$PATH
     - name: "macOS"
       os: osx
       before_install: python3 --version; pip3 --version; sw_vers
+      env:
+        - PY=python3 PATH=$HOME/.local/bin:$PATH
     - name: "Windows"
       os: windows
       before_install:
@@ -20,8 +21,7 @@ jobs:
         - python -m ensurepip
         - python -m pip install --upgrade pip
       env:
-        - PATH=/c/Python37:/c/Python37/Scripts:$PATH
-        - PY=python
+        - PY=python PATH=/c/Python37:/c/Python37/Scripts:$PATH
   allow_failures:
   - os: linux
   - os: windows