fix JuliaLang#5123

Author: JeffBezanson

base/path.jl

@@ -12,7 +12,7 @@ end
 @windows_only begin
     const path_separator    = "\\"
     const path_separator_re = r"[/\\]+"
-    const path_absolute_re  = r"^(?:\w+:)[/\\]"
+    const path_absolute_re  = r"^(?:\w+:)?[/\\]"
     const path_directory_re = r"(?:^|[/\\])\.{0,2}$"
     const path_dir_splitter = r"^(.*?)([/\\]+)([^/\\]*)$"
     const path_ext_splitter = r"^((?:.*[/\\])?(?:\.|[^/\\\.])[^/\\]*?)(\.[^/\\\.]*|)$"