Remove needless dependency management

The curses gem was updated to allow for noop requires, meaning when you
require it with ruby < 2.1.0 it doesn't explode anymore.
ruby/curses#1

Gemfile

@@ -3,5 +3,3 @@ source 'https://rubygems.org'
 # Specify your gem's dependencies in opsicle.gemspec
 gemspec
 
-gem 'curses' if RUBY_VERSION >= '2.1' || RUBY_PLATFORM == 'java'
-

opsicle.gemspec

@@ -24,6 +24,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "highline", "~> 1.6"
   spec.add_dependency "terminal-table", "~> 1.4"
   spec.add_dependency "minitar", "~> 0.5"
+  spec.add_dependency "curses", "~> 1.0"
 
   spec.add_development_dependency "bundler", "~> 1.3"
   spec.add_development_dependency "rake", "~> 10.1"