chore: regenerate README (#189)

This PR was generated using Autosynth. 🌈


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

```
2021-08-31 23:27:54,193 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-retail/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-31 23:27:55,170 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/bbe02823-3bbc-4071-8687-00981d239470/targets

- [ ] To automatically regenerate this PR, check this box. (May take up to 24 hours.)

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-retail.git",
-        "sha": "2ccce7fc4aad86a4b258242d45ee4f2d7fa9dede"
+        "sha": "9be2a54983aba170d4c40e51b9e61ec0b9d5681b"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "8032ab5a32471d85ece8fc261df16cc40fbfa4fb"
+        "sha": "9a238a0623879c3de129a376c6085d4a862f6eb9"
       }
     }
   ]

README.md

@@ -27,7 +27,7 @@ If you are using Maven, add this to your pom.xml file:
 If you are using Gradle without BOM, add this to your dependencies
 
 ```Groovy
-compile 'com.google.cloud:google-cloud-retail:2.0.1'
+implementation 'com.google.cloud:google-cloud-retail:2.0.1'
 ```
 
 If you are using SBT, add this to your dependencies