Update import order for unidecode vs text_unidecode (#126)

AS is `text_unidecode` is install_requires it is always present in the python environment, 
it makes sense to try import optinal dependency `unidecode` first, and only then fallback 
to `text_unidecode`.

slugify/slugify.py

@@ -4,9 +4,9 @@
 from html.entities import name2codepoint
 
 try:
-    import text_unidecode as unidecode
-except ImportError:
     import unidecode
+except ImportError:
+    import text_unidecode as unidecode
 
 __all__ = ['slugify', 'smart_truncate']