Bump github.com/gorilla/websocket from 1.4.1 to 1.5.3

Bumps [github.com/gorilla/websocket](https://github.com/gorilla/websocket) from 1.4.1 to 1.5.3.
- [Release notes](https://github.com/gorilla/websocket/releases)
- [Commits](gorilla/websocket@v1.4.1...v1.5.3)

---
updated-dependencies:
- dependency-name: github.com/gorilla/websocket
  dependency-version: 1.5.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

go.mod

@@ -2,4 +2,4 @@ module github.com/sourcegraph/jsonrpc2
 
 go 1.12
 
-require github.com/gorilla/websocket v1.4.1
+require github.com/gorilla/websocket v1.5.3

go.sum

@@ -1,2 +1,2 @@
-github.com/gorilla/websocket v1.4.1 h1:q7AeDBpnBk8AogcD4DSag/Ukw/KV+YhzLj2bP5HvKCM=
-github.com/gorilla/websocket v1.4.1/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
+github.com/gorilla/websocket v1.5.3 h1:saDtZ6Pbx/0u+bgYQ3q96pZgCzfhKXGPqt7kZ72aNNg=
+github.com/gorilla/websocket v1.5.3/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=