Move generated-code-dependencies to peerDependencies.

I'm tempted to remove these dependencies all together because at this
point ts-proto has many different flags that can change whether the
generated code actually does/does not use certain dependencies.

I.e. users using the "only types" output probably don't want
ts-proto to bring in any dependencies. I guess in that case, they
could be using ts-proto as a devDependency.

Fixes #147.

package.json

@@ -37,10 +37,12 @@
     "uglify-js": "^3.9.2"
   },
   "dependencies": {
+    "ts-poet": "^1.0.1"
+  },
+  "peerDependencies": {
     "@types/object-hash": "^1.3.0",
     "dataloader": "^1.4.0",
     "object-hash": "^1.3.1",
-    "protobufjs": "^6.8.8",
-    "ts-poet": "^1.0.1"
+    "protobufjs": "^6.8.8"
   }
 }