chore: regenerate README (#976)

This PR was generated using Autosynth. 🌈


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

```
2021-08-31 20:20:23,056 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigtable/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-31 20:20:24,399 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/9bfe71a9-b974-49ae-bf52-c140b7f7e2b1/targets

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

Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigtable.git",
-        "sha": "6bf1ad93f998546a1d642776765163858a474bc5"
+        "sha": "e5bb52eead42e8b351a7469529837d8b509b8332"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "31728d872f50e439ded2f67fa8d67955b26a4e35"
+        "sha": "9a238a0623879c3de129a376c6085d4a862f6eb9"
       }
     }
   ]

README.md

@@ -51,12 +51,12 @@ If you are using Gradle 5.x or later, add this to your dependencies
 ```Groovy
 implementation platform('com.google.cloud:libraries-bom:22.0.0')
 
-compile 'com.google.cloud:google-cloud-bigtable'
+implementation 'com.google.cloud:google-cloud-bigtable'
 ```
 If you are using Gradle without BOM, add this to your dependencies
 
 ```Groovy
-compile 'com.google.cloud:google-cloud-bigtable:2.1.0'
+implementation 'com.google.cloud:google-cloud-bigtable:2.1.0'
 ```
 
 If you are using SBT, add this to your dependencies