TextFormatter behaviour aligned with stdlib log (fixes #167)

stdlib `log` adds a newline at the end of a message if none is present,
otherwise does not. Before this change logrus would always add
a newline, resulting in inconsistent behaviour if stdlib log was
replaced with logrus, and a user would e.g. use 'log.printf("test\n")'

text_formatter.go

@@ -126,6 +126,10 @@ func (f *TextFormatter) printColored(b *bytes.Buffer, entry *Entry, keys []strin
 
 	levelText := strings.ToUpper(entry.Level.String())[0:4]
 
+	// Remove a single newline if it already exists in the message to keep
+	// the behavior of logrus text_formatter the same as the stdlib log package
+	entry.Message = strings.TrimSuffix(entry.Message, "\n")
+
 	if f.DisableTimestamp {
 		fmt.Fprintf(b, "\x1b[%dm%s\x1b[0m %-44s ", levelColor, levelText, entry.Message)
 	} else if !f.FullTimestamp {