feat: support optional proto3 fields

This was implemented in ts-protoc-gen in
improbable-eng/ts-protoc-gen#275 and released
nearly a year ago in [email protected]; glancing through the issue
history it looks like the only reason this hasn't been bumped yet is
because no one's tried to contribute it.

package.json

@@ -7,23 +7,23 @@
     "google-protobuf": "3.12.2"
   },
   "devDependencies": {
+    "@bazel/typescript": "3.0.0",
     "@bazel/concatjs": "3.0.0",
     "@bazel/jasmine": "3.0.0",
     "@bazel/rollup": "3.0.0",
-    "@bazel/typescript": "3.0.0",
-    "@grpc/grpc-js": "1.2.1",
     "@improbable-eng/grpc-web": "0.13.0",
     "@types/google-protobuf": "3.7.2",
     "@types/jasmine": "3.5.11",
     "@types/node": "12.12.50",
-    "c8": "^7.10.0",
+    "c8": "^7.3.0",
     "clang-format": "1.4.0",
-    "grpc": "1.24.9",
+    "grpc": "1.24.3",
     "grpc-tools": "1.10.0",
+    "@grpc/grpc-js": "1.2.1",
     "husky": "4.2.5",
-    "jasmine": "^3.10.0",
-    "jasmine-core": "^3.10.1",
-    "jasmine-reporters": "^2.5.0",
+    "jasmine": "^3.6.1",
+    "jasmine-core": "^3.6.0",
+    "jasmine-reporters": "^2.3.2",
     "karma": "5.0.1",
     "karma-chrome-launcher": "3.1.0",
     "karma-firefox-launcher": "1.3.0",
@@ -37,7 +37,7 @@
     "rollup-plugin-commonjs": "10.1.0",
     "rollup-plugin-node-resolve": "5.2.0",
     "source-map-support": "0.5.19",
-    "ts-protoc-gen": "0.14.0",
+    "ts-protoc-gen": "0.15.0",
     "tsickle": "0.39.1",
     "tsutils": "3.17.1",
     "typescript": "3.9.7",