gems: fix version require in gemspec (#10)

README.md

@@ -65,6 +65,8 @@ A part of the test suite is automatically generated from Keccak's reference test
 
 ## Warning: Keccak vs. SHA-3
 
+**Note:** This gem still uses the `Digest::SHA3` namespace for reasons of backwards compatibility and long-term maintainability. See history section below.
+
 :warning: This gem does **not** implement the final FIPS202 standard, today known as SHA-3 but rather an early version, commonly referred to as Keccak. The reason why this is kept around, is that Ethereum uses this earler version of Keccak. See also: [Ethereum: Difference between keccak256 and sha3](https://ethereum.stackexchange.com/questions/30369/difference-between-keccak256-and-sha3)
 
 If you are looking for the final SHA-3 gem, please use the following: https://rubygems.org/gems/sha3

keccak.gemspec

@@ -3,7 +3,7 @@
 lib = File.expand_path('lib', __dir__).freeze
 $LOAD_PATH.unshift lib unless $LOAD_PATH.include? lib
 
-require 'digest/sha3'
+require 'digest/sha3/version'
 
 Gem::Specification.new do |spec|
   spec.name = "keccak"