Handle process.stdout.columns being negative

Adam Miskiewicz reported a RangeError raised when running on
macOS 10.12, with Node 8.6.  This would would have been caused by
process.stdout.columns returning a negative number.

If the value is negative, assume a width of 100 characters (as present
in spinner-progress.js).

src/reporters/console/util.js

@@ -12,7 +12,8 @@ const CLEAR_RIGHT_OF_CURSOR = 1;
 export function clearLine(stdout: Stdout) {
   if (!supportsColor) {
     if (stdout instanceof tty.WriteStream) {
-      stdout.write(`\r${' '.repeat(stdout.columns - 1)}\r`);
+      const columns = stdout.columns > 0 ? stdout.columns : 100;
+      stdout.write(`\r${' '.repeat(columns - 1)}\r`);
     }
     return;
   }