Update for libgit2 v0.27

Author: carlosmn

.travis.sh

@@ -2,7 +2,7 @@
 
 cd ~
 
-git clone --depth=1 -b maint/v0.26 https://github.com/libgit2/libgit2.git
+git clone --depth=1 -b maint/v0.27 https://github.com/libgit2/libgit2.git
 cd libgit2/
 
 mkdir build && cd build

pygit2/config.py

@@ -219,7 +219,7 @@ def add_file(self, path, level=0, force=0):
         """Add a config file instance to an existing config."""
 
         err = C.git_config_add_file_ondisk(self._config, to_bytes(path), level,
-                                           force)
+                                           ffi.NULL, force)
         check_error(err)
 
     def snapshot(self):

pygit2/decl.h

@@ -572,6 +572,7 @@ int git_config_delete_entry(git_config *cfg, const char *name);
 int git_config_add_file_ondisk(git_config *cfg,
 	const char *path,
 	git_config_level_t level,
+	const git_repository *repo,
 	int force);
 
 int git_config_iterator_new(git_config_iterator **out, const git_config *cfg);