Don't count newline against commit subject length

When comparing the commit subject against the specified limit, trailing
newlines should not be considered part of a subject's character count.

lib/overcommit/hook/commit_msg/text_width.rb

@@ -7,7 +7,7 @@ def run
 
       @errors = []
 
-      find_errors_in_subject(commit_message_lines.first)
+      find_errors_in_subject(commit_message_lines.first.chomp)
       find_errors_in_body(commit_message_lines)
 
       return :warn, @errors.join("\n") if @errors.any?

spec/overcommit/hook/commit_msg/text_width_spec.rb

@@ -6,7 +6,7 @@
   subject { described_class.new(config, context) }
 
   before do
-    context.stub(:commit_message_lines).and_return(commit_msg.split("\n"))
+    context.stub(:commit_message_lines).and_return(commit_msg.lines)
     context.stub(:empty_message?).and_return(commit_msg.empty?)
   end
 
@@ -28,6 +28,16 @@
     it { should pass }
   end
 
+  context 'when the subject is 60 characters followed by a newline' do
+    let(:commit_msg) { <<-MSG }
+      This is 60 characters, or 61 if the newline is counted
+
+      A reasonable line.
+    MSG
+
+    it { should pass }
+  end
+
   context 'when a line in the message is 72 characters followed by a newline' do
     let(:commit_msg) { <<-MSG }
       Some summary