Highlight Jenkinsfile as groovy

Change-Id: I1d2c24945c07949eba3d2018dcc81b4edd634973
diff --git a/gerrit-server/src/main/resources/com/google/gerrit/server/mime/mime-types.properties b/gerrit-server/src/main/resources/com/google/gerrit/server/mime/mime-types.properties
index 996e8a4..baf1753 100644
--- a/gerrit-server/src/main/resources/com/google/gerrit/server/mime/mime-types.properties
+++ b/gerrit-server/src/main/resources/com/google/gerrit/server/mime/mime-types.properties
@@ -100,6 +100,7 @@
 intr = text/x-dylan
 jade = text/x-pug
 java = text/x-java
+Jenkinsfile = text/x-groovy
 jl = text/x-julia
 jruby = text/x-ruby
 js = text/javascript