Update jsonwebtoken dependency to 8.1.0

Author: tjanczuk

package.json

@@ -1,6 +1,6 @@
 {
   "name": "express-jwt",
-  "version": "5.3.0",
+  "version": "5.3.1",
   "description": "JWT authentication middleware.",
   "keywords": [
     "auth",
@@ -36,7 +36,7 @@
   "dependencies": {
     "async": "^1.5.0",
     "express-unless": "^0.3.0",
-    "jsonwebtoken": "^7.3.0",
+    "jsonwebtoken": "^8.1.0",
     "lodash.set": "^4.0.0"
   },
   "devDependencies": {