fix a index for "C" in libgit2.asc

Author: satob

book/B-embedding-git/sections/libgit2.asc

@@ -1,6 +1,6 @@
 === Libgit2
 
-(((libgit2)))(((C)))
+(((libgit2)))((("C")))
 Another option at your disposal is to use Libgit2.
 Libgit2 is a dependency-free implementation of Git, with a focus on having a nice API for use within other programs.
 You can find it at http://libgit2.github.com[].