Fix error in worker declaration example sniplet

With line:
```
  executable=ctx.attr.worker,
```
I got error like:
```
Error in run: in call to run(), parameter 'executable' got value of type 'Target', want 'File, string, or FilesToRunProvider'
```

site/docs/creating-workers.md

@@ -44,12 +44,12 @@ for singleplex workers.
 
 ```json
 {
-  “args” : [“--some_argument”],
-  “inputs” : [
-    { “/path/to/my/file/1” : “fdk3e2ml23d”},
-    { “/path/to/my/file/2” : “1fwqd4qdd” }
- ],
-  “request_id” : 12
+  "args" : ["--some_argument"],
+  "inputs" : [
+    { "/path/to/my/file/1" : "fdk3e2ml23d"},
+    { "/path/to/my/file/2" : "1fwqd4qdd" }
+  ],
+  "request_id" : 12
 }
 ```
 
@@ -70,10 +70,9 @@ to redirect the `stdout` of any tools it uses to `stderr`.
 
 ```json
 {
-  “exit_code” : 1,
-  “output” : “Action failed with the following message:\nCould not find input
-    file “/path/to/my/file/1”,
-  “request_id” : 12
+  "exit_code" : 1,
+  "output" : "Action failed with the following message:\nCould not find input file \"/path/to/my/file/1\"",
+  "request_id" : 12
 }
 ```
 
@@ -84,7 +83,7 @@ id, so the request id must be specified if it is nonzero. This is a valid
 
 ```json
 {
-  “request_id” : 12,
+  "request_id" : 12,
 }
 ```
 
@@ -215,13 +214,14 @@ startup args, the call to `ctx.actions.run` might be:
 ```python
 ctx.actions.run(
   inputs=ctx.files.srcs,
-  outputs=[ctx.attr.output],
-  executable=ctx.attr.worker,
+  outputs=[ctx.outputs.output],
+  executable=ctx.executable.worker,
   mnemonic="someMnemonic",
   execution_requirements={
-    “supports-workers” : “1”,
-    “requires-worker-protocol” : “json},
-  arguments=ctx.attr.args + [“@flagfile”]
+    "supports-workers" : "1",
+    "requires-worker-protocol" : "json",
+  },
+  arguments=ctx.attr.args + ["@flagfile"]
  )
 ```