use sad cmd.exe compatible equivalents for fun unicode status characters

vanilla windows terminal (cmd.exe) does not have robust unicode support
beyond the old ibm codepage 437.

the console team is aware and working on it..

- microsoft/WSL#75
- microsoft/terminal#104
- microsoft/terminal#190
- microsoft/terminal#226
- microsoft/terminal#306

Rakefile

@@ -26,7 +26,10 @@ def exec_with_echo(cmd)
 end
 
 def fail(message)
-  abort("✘ #{message}")
+  # win-safe:      desired:
+  #  √ - \u221A     ✓ - \u2713
+  #  × - \u00D7     ✘ - \u2718
+  abort("× #{message}")
 end
 
 def try(cmd, failure_message)