Add nightly crystal to a spec matrix

This project is very large and serves as a great test bed for breakages
in nightly builds of crystal

.github/workflows/ci.yml

@@ -26,13 +26,28 @@ jobs:
 
     runs-on: ubuntu-latest
 
+    name: "build - crystal: ${{ matrix.crystal }}, stable: ${{ matrix.stable }}"
+
+    continue-on-error: ${{ !matrix.stable }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        stable: [true]
+        crystal:
+          - 1.1.0
+          - 1.0.0
+        include:
+          - crystal: nightly
+            stable: false
+
     steps:
       - uses: actions/checkout@v2
 
       - name: Install Crystal
         uses: oprypin/install-crystal@v1.2.4
         with:
-          crystal: 1.0.0
+          crystal: ${{ matrix.crystal }}
 
       - name: Cache Shards
         uses: actions/cache@v2