rustfmt the repository rust-lang#398

Author: prertik

src/parse/summary.rs

@@ -57,7 +57,8 @@ fn parse_level(
                     ErrorKind::Other,
                     "Your summary.md is messed up\n\n
                         Prefix, \
-                                       Suffix and Spacer elements can only exist on the root level.\n
+                                       Suffix and Spacer elements can only exist \ 
+                                       on the root level.\n
                         \
                                        Prefix elements can only exist before any chapter and there can be \
                                        no chapters after suffix elements.",