Update dependency jsrsasign to v11 [SECURITY]

Author: renovate[bot]

amp-update-cache/package.json

@@ -12,7 +12,7 @@
   "dependencies": {
     "amp-toolbox-update-cache": "^1.0.0",
     "express": "^4.14.1",
-    "jsrsasign": "^8.0.0",
+    "jsrsasign": "^11.0.0",
     "mime-types": "^2.1.15",
     "multer": "^1.3.0",
     "node-fetch": "^2.0.0",