Refactor unit initialization and update dependencies (#380)

Author: olbrich

lib/ruby_units/cache.rb

@@ -20,6 +20,8 @@ def get(key)
     # @return [void]
     def set(key, value)
       key = key.to_unit.units unless key.is_a?(String)
+      return if should_skip_caching?(key)
+
       data[key] = value
     end
 
@@ -32,5 +34,9 @@ def keys
     def clear
       @data = {}
     end
+
+    def should_skip_caching?(key)
+      keys.include?(key) || key =~ RubyUnits::Unit.special_format_regex
+    end
   end
 end