Update .github/workflows

.github/workflows/ci.yml

@@ -51,7 +51,7 @@ jobs:
             os: ubuntu-18.04
           - toolset: clang
             compiler: clang++-3.5
-            cxxstd: "03,11,14"
+            cxxstd: "03,11"
             os: ubuntu-16.04
             install: clang-3.5
           - toolset: clang