fix(grpc): loosen version range on @grpc/grpc-js (#153)

The strict `~` version range on `@grpc/grpc-js` makes `grpc-gcp` difficult to use in conjunction with `gax`, because libraries must be upgraded in step with each other.

Let's leave the dependency strict in gax, but loose in `grpc-gcp`.

_Note: also upgraded mocha to address security warning._

package.json

@@ -32,7 +32,7 @@
     "node": ">=12"
   },
   "dependencies": {
-    "@grpc/grpc-js": "~1.7.0"
+    "@grpc/grpc-js": "^1.7.0"
   },
   "devDependencies": {
     "@grpc/proto-loader": "^0.7.0",
@@ -44,7 +44,7 @@
     "grpc": "^1.24.10",
     "grpc-tools": "^1.11.1",
     "gts": "^3.1.0",
-    "mocha": "^8.4.0",
+    "mocha": "^9.2.2",
     "typescript": "^4.3.2"
   },
   "files": [