Use correct quotes

Author: lukel97

.github/workflows/haskell.yml

@@ -13,7 +13,7 @@ jobs:
 
  steps:
  - name: Install ghc and cabal-install
- if: startsWith(matrix.os, "macOS")
+ if: startsWith(matrix.os, 'macOS')
  run: brew install ghc cabal-install
  - uses: actions/checkout@v1
  with: