chore: update gapic-generator-java version to 2.1.0 (#522)

PiperOrigin-RevId: 391407209

Source-Author: Google APIs <noreply@google.com>
Source-Date: Tue Aug 17 16:48:10 2021 -0700
Source-Repo: googleapis/googleapis
Source-Sha: e1738ee972b49fd0c4d4718b035444495142b781
Source-Link: googleapis/googleapis@e1738ee

Co-authored-by: Emily Ball <emilyball@google.com>

synth.metadata

@@ -11,24 +11,24 @@
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "d9eaf41de44d953458b18712a3f240bb4c564e48",
-        "internalRef": "388535346"
+        "sha": "e1738ee972b49fd0c4d4718b035444495142b781",
+        "internalRef": "391407209"
       }
     },
     {
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "d9eaf41de44d953458b18712a3f240bb4c564e48",
-        "internalRef": "388535346"
+        "sha": "e1738ee972b49fd0c4d4718b035444495142b781",
+        "internalRef": "391407209"
       }
     },
     {
       "git": {
         "name": "googleapis",
         "remote": "https://github.com/googleapis/googleapis.git",
-        "sha": "d9eaf41de44d953458b18712a3f240bb4c564e48",
-        "internalRef": "388535346"
+        "sha": "e1738ee972b49fd0c4d4718b035444495142b781",
+        "internalRef": "391407209"
       }
     },
     {