chore: regenerate README (#946)

This PR was generated using Autosynth. 🌈


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

```
2021-08-10 18:09:57,347 synthtool [DEBUG] > Executing /root/.cache/synthtool/java-bigtable/.github/readme/synth.py.
On branch autosynth-readme
nothing to commit, working tree clean
2021-08-10 18:09:58,581 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/d636680c-27ae-481a-81b8-6def71087121/targets

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Author: yoshi-automation

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

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/java-bigtable.git",
-        "sha": "bc73916675c720a8ade9192594f914508bff0eda"
+        "sha": "3db12b2bc17c14f24952c241e065e45fa530dab4"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "3d32990b6f4b57be77455e3ca89e6e21cd0c06b3"
+        "sha": "6252f2cd074c38f37b44abe5e96d128733eb1b61"
       }
     }
   ]

README.md

@@ -56,13 +56,13 @@ compile '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:1.27.3'
+compile 'com.google.cloud:google-cloud-bigtable:2.0.0'
 ```
 
 If you are using SBT, add this to your dependencies
 
 ```Scala
-libraryDependencies += "com.google.cloud" % "google-cloud-bigtable" % "1.27.3"
+libraryDependencies += "com.google.cloud" % "google-cloud-bigtable" % "2.0.0"
 ```
 
 ## Authentication