Always reset ANSI colors in progress-bar line

When having a message like `waiting for a machine to build X` and
building with `nix build -L`, the log-prefix is always colored yellow[1]
on a small terminal-width as everything (including the ANSI color-reset) is
stripped away.

To work around that problem, this patch explicitly adds an `ANSI_NORMAL`
to the end of the line.

[1] https://imgur.com/a/FjtJOk3

src/libmain/progress-bar.cc

@@ -362,7 +362,7 @@ public:
         auto width = getWindowSize().second;
         if (width <= 0) width = std::numeric_limits<decltype(width)>::max();
 
-        writeToStderr("\r" + filterANSIEscapes(line, false, width) + "\e[K");
+        writeToStderr("\r" + filterANSIEscapes(line, false, width) + ANSI_NORMAL + "\e[K");
     }
 
     std::string getStatus(State & state)