Typo in ci.yml (#117)

Author: rafie

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     strategy:
       matrix:
         platform: ['ubuntu-20.04', 'ubuntu-18.04', 'ubuntu-16.04']
-        python: ['3.6', '3.7', '3.8' '3.9']
+        python: ['2.7', '3.6', '3.7', '3.8', '3.9']
 
     steps:
     - uses: actions/checkout@v2