Fixed problem in "merb-gen migration" that failed because the destination directory was nil.
Fixed problem in "merb-gen migration" that failed because the destination directory was nil.

Running "merb-gen migration AddMyStuff" failed with "can't convert nil into String".
This happened because RubyGen needs to know the application root (which was nil). I fixed it
by passing the application root in the initialisation options for Rubygen.

Signed-off-by: Michael D. Ivey <61b7b289766e9ecebf0145c0b7e626d828d24330@gweezlebur.com>

merb/merb-gen,merb/merb-gen