fix the revision of AssemblyScript; the latest one has lots of incompatible changes

Author: gfx

package-lock.json

@@ -59,7 +59,7 @@
     "@types/node": "^12.0.4",
     "@typescript-eslint/eslint-plugin": "^1.9.0",
     "@typescript-eslint/parser": "^1.9.0",
-    "assemblyscript": "github:AssemblyScript/assemblyscript",
+    "assemblyscript": "github:AssemblyScript/assemblyscript#5269a6b9c4e14983c43671328257c156cdf1de8a",
     "assert": "^2.0.0",
     "core-js": "^3.1.3",
     "eslint": "^5.16.0",