Update Swift to 5.1.4 (#119)

diff --git a/core/swift51Action/Dockerfile b/core/swift51Action/Dockerfile
index c6aa303..947f44c 100644
--- a/core/swift51Action/Dockerfile
+++ b/core/swift51Action/Dockerfile
@@ -28,7 +28,7 @@
   && cd openwhisk-runtime-go-*/main\
   && GO111MODULE=on go build -o /bin/proxy
 
-FROM swift:5.1.2
+FROM swift:5.1.4
 
 # select the builder to use
 ARG GO_PROXY_BUILD_FROM=release