try to use xcode 11 beta

.github/workflows/ci.yml

@@ -3,6 +3,10 @@ on: [push, pull_request]
 jobs:
   test:
     runs-on: macos-latest
+    name: Test ${{ matrix.xcode }}
+    strategy:
+      matrix:
+        xcode: [Xcode_10.3, Xcode_11_beta]
     steps:
     - uses: actions/checkout@master
     - name: Info
@@ -10,7 +14,6 @@ jobs:
         swift --version
         swift package --version
         xcode-select -p
-        ls /Applications
     - name: Resolve
       run: swift package resolve
     - name: Build