[Gemspec] Include the changelog of RCs in the post install message

cocoapods.gemspec

@@ -49,11 +49,16 @@ s.files = Dir["lib/**/*.rb"] + %w{ bin/pod bin/sandbox-pod README.md LICENSE CHA
   changelog_path = File.expand_path('../CHANGELOG.md', __FILE__)
   if File.exists?(changelog_path)
     title_token = '## '
-    current_verison_title = title_token + Pod::VERSION.to_s
-    full_changelog = File.open(changelog_path, "r:UTF-8") { |f| f.read }
-    current_version_index = full_changelog.index(/^#{current_verison_title}/)
-    previous_version_index = full_changelog.index(/^#{title_token}/, current_version_index + title_token.length)
-    relevant = full_changelog[current_version_index..previous_version_index-1]
-    s.post_install_message = "\nCHANGELOG:\n\n" + relevant + "\n"
+    current_verison_title = title_token +  Pod::VERSION.to_s
+    text = File.open(changelog_path, "r:UTF-8") { |f| f.read }
+    lines = text.split("\n")
+
+    current_version_index = lines.find_index { |line| line =~ (/^#{current_verison_title}/) }
+    previous_version_lines = lines[(current_version_index+1)...-1]
+    previous_version_index = current_version_index + previous_version_lines.find_index { |line| line =~ (/^#{title_token}/) && !line.include?('rc') }
+
+    relevant = lines[current_version_index..previous_version_index]
+
+    s.post_install_message = "\nCHANGELOG:\n\n" + relevant.join("\n") + "\n"
   end
 end