Set --dirty to .1.dirty in git describe call

Without this patch, if you've tagged v1.2.3, and then off that make some
edits, GVB.version would then be 1.2.3.dirty.  The problem is that RubyGems
treats a string as being LESS THAN ZERO, so 1.2.3.dirty < 1.2.3.  In order
to make a dirty tree based off v1.2.3 be considered a newer version than
1.2.3, we need to make the version 1.2.3.1.dirty, which is what
--dirty='.1.dirty' does for us.

lib/git-version-bump.rb

@@ -34,7 +34,7 @@ def self.caller_gemspec
 	end
 
 	def self.version(gem = nil)
-		git_ver = `git describe --dirty --match='v[0-9]*.[0-9]*.*[0-9]' 2>/dev/null`.
+		git_ver = `git describe --dirty='.1.dirty' --match='v[0-9]*.[0-9]*.*[0-9]' 2>/dev/null`.
 		            strip.
 		            gsub(/^v/, '').
 		            gsub('-', '.')