chore: regenerate README (#554)

This PR was generated using Autosynth. 🌈


<details><summary>Log from Synthtool</summary>

```
2020-12-06 23:23:25,168 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquerydatatransfer/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2020-12-06 23:23:26,051 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

Full log will be available here:
https://source.cloud.google.com/results/invocations/0d840010-880f-4541-a540-02c3d28eb9bd/targets

- [ ] To automatically regenerate this PR, check this box.

.github/readme/synth.metadata/synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquerydatatransfer.git",
-        "sha": "18e069fd0dc437ba5254a6b412bad91bfc9b7a5f"
+        "sha": "326a9c3093e847f3e1441a40f778292af8331b03"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "91b34d7ffc37581e03eec8b16d08b84e46b82bbe"
+        "sha": "18c5dbdb4ac8cf75d4d8174e7b4558f48e76f8a1"
       }
     }
   ]

README.md

@@ -38,18 +38,18 @@ If you are using Maven without BOM, add this to your dependencies:
 <dependency>
   <groupId>com.google.cloud</groupId>
   <artifactId>google-cloud-bigquerydatatransfer</artifactId>
-  <version>1.0.20</version>
+  <version>1.0.21</version>
 </dependency>
 
 ```
 
 If you are using Gradle, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-bigquerydatatransfer:1.0.20'
+compile 'com.google.cloud:google-cloud-bigquerydatatransfer:1.0.21'
 ```
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-bigquerydatatransfer" % "1.0.20"
+libraryDependencies += "com.google.cloud" % "google-cloud-bigquerydatatransfer" % "1.0.21"
 ```
 
 ## Authentication