Update version for 1.9.1 development.

Author: gbrail

gradle.properties

@@ -1,6 +1,6 @@
 rootProject.name=rhino-root
 group=org.mozilla
-version=1.9.0
+version=1.9.1-SNAPSHOT
 mavenReleaseRepo=https://oss.sonatype.org/service/local/staging/deploy/maven2/
 mavenSnapshotRepo=https://oss.sonatype.org/content/repositories/snapshots
 githubPackagesRepo=https://maven.pkg.github.com/mozilla/rhino