Add swift 4&5

Author: MrLotU

circle.yml

@@ -1,6 +1,22 @@
 version: 2
 
 jobs:
+  swift4:
+    docker:
+      - image: swift:4.2
+    steps:
+      - checkout
+      - run: apt-get update; apt-get install -y libssl-dev zlib1g-dev
+      - run: swift build
+      - run: swift test
+  swift5:
+    docker:
+      - image: swift:5
+    steps:
+      - checkout
+      - run: apt-get update; apt-get install -y libssl-dev zlib1g-dev
+      - run: swift build
+      - run: swift test
   bionic:
     docker:
       - image: vapor/swift:5.1-bionic
@@ -22,4 +38,6 @@ workflows:
   tests:
     jobs:
       - bionic
-      - bionic-release
+      - bionic-release
+      - swift4
+      - swift5