Add Go 1.14, force module support in Travis

.travis.yml

@@ -4,6 +4,9 @@ go:
     - 1.11.x
     - 1.12.x
     - 1.13.x
+    - 1.14.x
+env:
+    - GO111MODULE=on
 install:
     - go get github.com/bwmarrin/discordgo
     - go get -v .