Rid of warning in Rico

When using rico with warnings in ruby enabled (the -w option) it spews lots of warnings about using the @component_instance field when it's not initialized.

The one-line patch below simply initializes it to nil.

(There's no separate Jira project for Rico, nor is there a component for it, but this seemed like the right place anyway).

Index: rico/componentspecification.rb
===================================================================
RCS file: /cvsroot/picocontainer/rico/rico/componentspecification.rb,v
retrieving revision 1.10
diff -r1.10 componentspecification.rb
12a13
> @component_instance = nil
54c55
< end
\ No newline at end of file
—
> end