chore: convert version.txt to versions.txt for expected release-please format

chingor13 · chingor13 · commit 2e917e97b3bc · 2020-07-01T11:29:59.000-07:00
diff --git a/build.gradle b/build.gradle
@@ -27,7 +27,7 @@ apply plugin: 'io.codearte.nexus-staging'
 group = "com.google.api"
 archivesBaseName = "api-common"
 
-project.version = new File("version.txt").text.trim()
+project.version = "1.9.3-SNAPSHOT" // {x-version-update:api-common:current}
 
 sourceCompatibility = 1.7
 targetCompatibility = 1.7
diff --git a/version.txt b/version.txt
diff --git a/versions.txt b/versions.txt
@@ -0,0 +1,4 @@
+# Format:
+# module:released-version:current-version
+
+api-common:1.9.2:1.9.3-SNAPSHOT
