Merge pull request #33 from chriskrycho/patch-1

Fix spelling of "procedural" in table of contents.

Author: steveklabnik

src/SUMMARY.md

@@ -16,7 +16,7 @@
 
 - [Macros](macros.md)
     - [Macros By Example](macros-by-example.md)
-    - [Procedrual Macros](procedural-macros.md)
+    - [Procedural Macros](procedural-macros.md)
 
 - [Crates and source files](crates-and-source-files.md)