Drop unsupported Ruby

Author: JonRowe

ci/.github/workflows/ci.yml

@@ -21,8 +21,6 @@ jobs:
           - 2.5
           - 2.4
           - 2.3
-          - 2.2
-          - 2.1.9
           - ruby-head
         env:
           -
@@ -36,14 +34,6 @@ jobs:
             os: ubuntu-18.04
             env:
               JRUBY_OPTS: "--dev"
-          - ruby: 2.7
-            name_extra: "with diff-lcs 1.3"
-            env:
-              DIFF_LCS_VERSION: "~> 1.3.0"
-          - ruby: 2.7
-            name_extra: "with diff-lcs 1.4.3"
-            env:
-              DIFF_LCS_VERSION: "1.4.3"
       fail-fast: false
     continue-on-error: ${{ matrix.allow_failure || endsWith(matrix.ruby, 'head') }}
     env: ${{ matrix.env }}
@@ -69,8 +59,6 @@ jobs:
           - 2.5
           - 2.4
           - 2.3
-          - 2.2
-          - 2.1.9
       fail-fast: false
     steps:
       - uses: actions/checkout@v2