Fix blobs for file services

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/services/files/create_service.rb

@@ -24,7 +24,8 @@ module Files
         return error("Your changes could not be committed, because file name contains not allowed characters")
       end
 
-      blob = repository.blob_at(ref, file_path)
+      commit = repository.commit(ref)
+      blob = repository.blob_at(commit.sha, file_path)
 
       if blob
         return error("Your changes could not be committed, because file with such name exists")

app/services/files/delete_service.rb

@@ -17,7 +17,8 @@ module Files
         return error("You can only create files if you are on top of a branch")
       end
 
-      blob = repository.blob_at(ref, path)
+      commit = repository.commit(ref)
+      blob = repository.blob_at(commit.sha, path)
 
       unless blob
         return error("You can only edit text files")

app/services/files/update_service.rb

@@ -17,7 +17,8 @@ module Files
         return error("You can only create files if you are on top of a branch")
       end
 
-      blob = repository.blob_at(ref, path)
+      commit = repository.commit(ref)
+      blob = repository.blob_at(commit.sha, path)
 
       unless blob
         return error("You can only edit text files")