docs: update return type in jsdoc for Buffers (#159)

Author: yoshi-automation

packages/google-cloud-asset/src/v1/doc/google/iam/v1/doc_policy.js

@@ -71,7 +71,7 @@
  *
  *   This object should have the same structure as [Binding]{@link google.iam.v1.Binding}
  *
- * @property {string} etag
+ * @property {Buffer} etag
  *   `etag` is used for optimistic concurrency control as a way to help
  *   prevent simultaneous updates of a policy from overwriting each other.
  *   It is strongly suggested that systems make use of the `etag` in the

packages/google-cloud-asset/src/v1/doc/google/protobuf/doc_any.js

@@ -125,7 +125,7 @@
  *   Schemes other than `http`, `https` (or the empty scheme) might be
  *   used with implementation specific semantics.
  *
- * @property {string} value
+ * @property {Buffer} value
  *   Must be a valid serialized protocol buffer of the above specified type.
  *
  * @typedef Any

packages/google-cloud-asset/src/v1beta1/doc/google/iam/v1/doc_policy.js

@@ -71,7 +71,7 @@
  *
  *   This object should have the same structure as [Binding]{@link google.iam.v1.Binding}
  *
- * @property {string} etag
+ * @property {Buffer} etag
  *   `etag` is used for optimistic concurrency control as a way to help
  *   prevent simultaneous updates of a policy from overwriting each other.
  *   It is strongly suggested that systems make use of the `etag` in the

packages/google-cloud-asset/src/v1beta1/doc/google/protobuf/doc_any.js

@@ -125,7 +125,7 @@
  *   Schemes other than `http`, `https` (or the empty scheme) might be
  *   used with implementation specific semantics.
  *
- * @property {string} value
+ * @property {Buffer} value
  *   Must be a valid serialized protocol buffer of the above specified type.
  *
  * @typedef Any

packages/google-cloud-asset/synth.metadata

@@ -1,19 +1,19 @@
 {
-  "updateTime": "2019-06-05T14:12:31.290419Z",
+  "updateTime": "2019-06-12T11:09:03.735749Z",
   "sources": [
     {
       "generator": {
         "name": "artman",
-        "version": "0.23.1",
-        "dockerImage": "googleapis/artman@sha256:9d5cae1454da64ac3a87028f8ef486b04889e351c83bb95e83b8fab3959faed0"
+        "version": "0.24.1",
+        "dockerImage": "googleapis/artman@sha256:6018498e15310260dc9b03c9d576608908ed9fbabe42e1494ff3d827fea27b19"
       }
     },
     {
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "47c142a7cecc6efc9f6f8af804b8be55392b795b",
-        "internalRef": "251635729"
+        "sha": "f117dac435e96ebe58d85280a3faf2350c4d4219",
+        "internalRef": "252714985"
       }
     },
     {