remove other os

Issue: #10

.travis.yml

@@ -2,37 +2,16 @@ dist: xenial   # required for Python >= 3.7
 language: python
 matrix:
   include:
-    - name: "Python 3.7.1 on Xenial Linux"
-      python: 3.7
-      dist: xenial
     - name: "Python 3.7.2 on macOS"
       os: osx
       python: 3.7
       osx_image: xcode10.2
       language: shell
-    - name: "Python 3.7.3 on Windows"
-      os: windows
-      python: 3.7
-      language: shell
-      before_install: choco install python --version 3.7.3
-      env: PATH=/c/Python37:/c/Python37/Scripts:$PATH
-    - name: "Python 3.6 on Xenial Linux"
-      python: 3.6
-      dist: xenial
     - name: "Python 3.6 on macOS"
       os: osx
       python: 3.6
       osx_image: xcode10.2
       language: shell
-    - name: "Python 3.6 on Windows"
-      os: windows
-      python: 3.6
-      language: shell
-      before_install: choco install python --version 3.6.7
-      env: PATH=/c/Python36:/c/Python36/Scripts:$PATH
-    - name: "Python 3.5 on Linux"
-      python: 3.5
-
 install:
   - pip3 install -r requirements.txt
 script: