refactor(techStackGeneric): ignore .git directory (#253)

A significant fraction of the tech stack detection execution time was
often from scanning files in any `.git` directory. Prevent that.

Clearly, the speedup here depends on the relative size of the `.git`
directory versus the rest of the data. But at least on one machine,
this commit is a 2x speedup for running in the chalk repo:

    chalk insert --use-tech-stack-detection ./foo

We should eventually improve the directory walking here, and consider
ignoring other directories and files, but let's just do this for now.

Refs: #249

src/plugins/techStackGeneric.nim

@@ -179,7 +179,7 @@ proc scanDirectory(directory: string, category: string, subcategory: string) =
       break
     if kind == pcFile:
       scanFile(path, category, subcategory)
-    elif kind == pcDir:
+    elif kind == pcDir and not path.endsWith(".git"):
       scanDirectory(path, category, subcategory)
 
 proc getLanguages(directory: string, langs: var HashSet[string]) =
@@ -188,7 +188,7 @@ proc getLanguages(directory: string, langs: var HashSet[string]) =
       let ext = path.splitFile().ext
       if ext != "" and ext in languages:
         langs.incl(languages[ext])
-    elif kind == pcDir:
+    elif kind == pcDir and not path.endsWith(".git"):
       getLanguages(path, langs)
 
 proc detectLanguages(): HashSet[string] =