chore: regenerate README (#822)

This PR was generated using Autosynth. 🌈


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

```
2021-05-11 04:15:20,919 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigquerydatatransfer/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-05-11 04:15:22,265 synthtool [DEBUG] > Wrote metadata to .github/readme/synth.metadata/synth.metadata.

```
</details>

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Author: yoshi-automation

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

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigquerydatatransfer.git",
-        "sha": "a71020b5056ec3e42fe2b8cd08673d1bf9b01d81"
+        "sha": "0809ecb05df42393b60200d76ecd8e1efef34df6"
       }
     },
     {

README.md

@@ -51,12 +51,12 @@ compile 'com.google.cloud:google-cloud-bigquerydatatransfer'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 ```Groovy
-compile 'com.google.cloud:google-cloud-bigquerydatatransfer:1.2.12'
+compile 'com.google.cloud:google-cloud-bigquerydatatransfer:1.2.13'
 ```
 
 If you are using SBT, add this to your dependencies
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-bigquerydatatransfer" % "1.2.12"
+libraryDependencies += "com.google.cloud" % "google-cloud-bigquerydatatransfer" % "1.2.13"
 ```
 
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