[color] attempt Win newline fix

Appveyor fails with os.linesep in fstring

Author: chrissimpkins

lib/fdiff/color.py

@@ -24,13 +24,13 @@ def color_unified_diff_line(line):
     on the unified diff line type."""
     if line[0:2] == "+ ":
         return f"{green_start}{line}{reset}"
-    elif line == f"+{os.linesep}":
+    elif line == "+\n":
         # some lines are formatted as hyphen only with no other characters
         # this indicates an added empty line
         return f"{green_start}{line}{reset}"
     elif line[0:2] == "- ":
         return f"{red_start}{line}{reset}"
-    elif line == f"-{os.linesep}":
+    elif line == "-\n":
         # some lines are formatted as hyphen only with no other characters
         # this indicates a deleted empty line
         return f"{red_start}{line}{reset}"