ci update (#21)

Author: mateuszbaran

.github/workflows/ci.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        julia-version: [1.0, 1.1, 1.2, 1.3, 1.4, '~1.5.0-0']
+        julia-version: ['1.0', '1.1', '1.2', '1.3', '1.4', '~1.5.0-0']
         os: [ubuntu-latest, macOS-latest, windows-latest]
     steps:
       - uses: actions/checkout@v2