fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-AXIOS-174505

Author: snyk-test

package.json

@@ -32,7 +32,7 @@
   "homepage": "https://github.com/cloudevents/sdk-javascript#readme",
   "dependencies": {
     "ajv": "^6.7.0",
-    "axios": "0.18.0",
+    "axios": "0.18.1",
     "is-empty": "1.2.0",
     "uri-js": "4.2.2",
     "uuid": "3.3.2"