server: terminal width should fallback to 80x25. (#1895)

Some environments might disable access to `/dev/tty`, fall
back to '80' in such scenarios.

Move to 'cheggaaa/pb' package for better cross platform
support on fetching terminal width.

Fixes #1891

vendor/github.com/cheggaaa/pb/runecount.go

@@ -0,0 +1,17 @@
+package pb
+
+import (
+	"regexp"
+	"unicode/utf8"
+)
+
+// Finds the control character sequences (like colors)
+var ctrlFinder = regexp.MustCompile("\x1b\x5b[0-9]+\x6d")
+
+func escapeAwareRuneCountInString(s string) int {
+	n := utf8.RuneCountInString(s)
+	for _, sm := range ctrlFinder.FindAllString(s, -1) {
+		n -= len(sm)
+	}
+	return n
+}