fix(windows): corrects issue with glob missing lowercase drive letters (#370)

Co-authored-by: Mike Iversen <[email protected]>

Author: miversen33

lua/plenary/path.lua

@@ -78,7 +78,7 @@ end
 
 local is_absolute = function(filename, sep)
   if sep == "\\" then
-    return string.match(filename, "^[A-Z]:\\.*$")
+    return string.match(filename, "^[%a]:\\.*$")
   end
   return string.sub(filename, 1, 1) == sep
 end