help.rb line_contract misnamed

[davebytemfg]

Without looking at what this is used for, I'm guessing this change is more correct.
Because there's already a label_contract that looks correct.

diff --git a/dragon/help.rb b/dragon/help.rb
index aee60d8..f2cd577 100644
--- a/dragon/help.rb
+++ b/dragon/help.rb
@@ -45,7 +45,7 @@ S
 S
     end
 
-    def self.label_contract
+    def self.line_contract
       <<-S
 * :line (if :primitive_marker returns :line)
 ** :x, :y, :x2, :y2, :r, :g, :b, :a