add missing dependency

Author: jdeantoni

plugins/gexpressions/org.eclipse.gemoc.gexpressions.xtext/META-INF/MANIFEST.MF

@@ -16,7 +16,8 @@ Require-Bundle: org.eclipse.xtext;visibility:=reexport,
  org.eclipse.equinox.common,
  org.eclipse.xtext.util,
  org.eclipse.xtext.xbase.lib,
- org.antlr.runtime
+ org.antlr.runtime,
+ org.eclipse.xtext.generator;bundle-version="2.27.0"
 Import-Package: org.apache.log4j
 Bundle-RequiredExecutionEnvironment: JavaSE-1.8
 Export-Package: org.eclipse.gemoc.gexpressions.xtext,