update version of tomcat 7 used in plugin

I've spent a bit of timing figuring out why our JSF listeners get registered twice when run within the IDE, but not our test servers. I believe I've found the reason; this bug - https://bz.apache.org/bugzilla/show_bug.cgi?id=55282#c9

When we run our app on our test servers (which use Tomcat 7.0.37) the listeners are registered just once. But running locally within the IDE, they register twice (tomcat7 maven plugin uses Tomcat 7.0.47). The bug was introduced in TC 7.0.42, and fixed in TC 7.0.55

When you next release the tomcat7 plugin, please consider updating the TC version used.