remove image_science as a dependancy

fotos.gemspec

@@ -32,7 +32,6 @@ Gem::Specification.new do |spec|
   spec.executables = "fotos"
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "image_science", "~> 1.3"
   spec.add_dependency "rubyzip", "~> 2.4"
   spec.add_dependency "rake", "~> 13.2"
   spec.add_dependency "ruby-vips", "~> 2.2"