Revert mocha to version 1.1

We seem to have had some spec example failures following an earlier bump of mocha from 1.1 to 1.4.

Reverting this seems to get rid of these failures.

dicom.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency('bundler', '~> 1.16')
   s.add_development_dependency('mini_magick', '~> 4.8')
-  s.add_development_dependency('mocha', '~> 1.4')
+  s.add_development_dependency('mocha', '~> 1.1')
   s.add_development_dependency('numo-narray', '~> 0.9', '>= 0.9.1.1')
   s.add_development_dependency('rake', '~> 12.3')
   s.add_development_dependency('redcarpet', '~> 3.4')