Release v1.6.0 (#324)

* Update version and changelog for v1.6.0
* Update docs
diff --git a/docs/dyn/cloudbuild_v1.operations.html b/docs/dyn/cloudbuild_v1.operations.html
index 493f9a6..88d0263 100644
--- a/docs/dyn/cloudbuild_v1.operations.html
+++ b/docs/dyn/cloudbuild_v1.operations.html
@@ -75,6 +75,9 @@
 <h1><a href="cloudbuild_v1.html">Google Cloud Container Builder API</a> . <a href="cloudbuild_v1.operations.html">operations</a></h1>
 <h2>Instance Methods</h2>
 <p class="toc_element">
+  <code><a href="#cancel">cancel(name, body, x__xgafv=None)</a></code></p>
+<p class="firstline">Starts asynchronous cancellation on a long-running operation.  The server</p>
+<p class="toc_element">
   <code><a href="#get">get(name, x__xgafv=None)</a></code></p>
 <p class="firstline">Gets the latest state of a long-running operation.  Clients can use this</p>
 <p class="toc_element">
@@ -85,6 +88,47 @@
 <p class="firstline">Retrieves the next page of results.</p>
 <h3>Method Details</h3>
 <div class="method">
+    <code class="details" id="cancel">cancel(name, body, x__xgafv=None)</code>
+  <pre>Starts asynchronous cancellation on a long-running operation.  The server
+makes a best effort to cancel the operation, but success is not
+guaranteed.  If the server doesn't support this method, it returns
+`google.rpc.Code.UNIMPLEMENTED`.  Clients can use
+Operations.GetOperation or
+other methods to check whether the cancellation succeeded or whether the
+operation completed despite cancellation. On successful cancellation,
+the operation is not deleted; instead, it becomes an operation with
+an Operation.error value with a google.rpc.Status.code of 1,
+corresponding to `Code.CANCELLED`.
+
+Args:
+  name: string, The name of the operation resource to be cancelled. (required)
+  body: object, The request body. (required)
+    The object takes the form of:
+
+{ # The request message for Operations.CancelOperation.
+  }
+
+  x__xgafv: string, V1 error format.
+    Allowed values
+      1 - v1 error format
+      2 - v2 error format
+
+Returns:
+  An object of the form:
+
+    { # A generic empty message that you can re-use to avoid defining duplicated
+      # empty messages in your APIs. A typical example is to use it as the request
+      # or the response type of an API method. For instance:
+      #
+      #     service Foo {
+      #       rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);
+      #     }
+      #
+      # The JSON representation for `Empty` is empty JSON object `{}`.
+  }</pre>
+</div>
+
+<div class="method">
     <code class="details" id="get">get(name, x__xgafv=None)</code>
   <pre>Gets the latest state of a long-running operation.  Clients can use this
 method to poll the operation result at intervals as recommended by the API