Separate the PRERELEASE version part with a dash instead of a dot

lib/rackstash/version.rb

@@ -18,9 +18,6 @@ module Rackstash
     # versions like beta or RC releases.
     PRERELEASE = 'dev'.freeze
 
-    # A standard string representation of the version parts
-    STRING = [MAJOR, MINOR, PATCH, PRERELEASE].compact.join('.').freeze
-
     # @return [Gem::Version] the version of the currently loaded Rackstash as
     #   a `Gem::Version`
     def self.gem_version
@@ -30,8 +27,15 @@ module Rackstash
     # @return [String] the Rackstash version as a semver-compliant string
     # @see http://semver.org/
     def self.to_s
-      STRING
+      @version ||= begin
+        base_version = [MAJOR, MINOR, PATCH].compact.join('.')
+        release = [base_version, PRERELEASE].compact.join('-')
+        release.freeze
+      end
     end
+
+    # A standard string representation of the version parts
+    STRING = to_s
   end
 
   # The Rackstash version as a semver-compliant string

spec/rackstash/version_spec.rb

@@ -10,6 +10,7 @@ require 'rackstash/version'
 describe 'Rackstash::Version' do
   it 'has a version number' do
     expect(Rackstash::Version::STRING).to be_a String
+    expect(Rackstash::Version::STRING).to equal Rackstash::Version.to_s
   end
 
   it 'exposes the version as Rackstash::VERSION' do
@@ -18,6 +19,7 @@ describe 'Rackstash::Version' do
 
   it 'exposes a gem_version method' do
     expect(Rackstash::Version.gem_version).to be_a Gem::Version
-    expect(Rackstash::Version.gem_version.to_s).to eql Rackstash::VERSION
+    expect(Rackstash::Version.gem_version.to_s.gsub('.pre.', '-'))
+      .to eql Rackstash::VERSION
   end
 end