[CircleCI] Add Swift 4.0 and 4.1 jobs

.circleci/config.yml

@@ -31,6 +31,12 @@ workflows:
   workflow:
     jobs:
       - xcode_codecov
+      - test_with_image:
+          name: linux_swift_4.0
+          image: norionomura/swift:4.0
+      - test_with_image:
+          name: linux_swift_4.1
+          image: norionomura/swift:4.1
       - test_with_image:
           name: linux_swift_4.2
           image: norionomura/swift:4.2