Fixes typo in WithField documentation

logger.go

@@ -53,7 +53,7 @@ func New() *Logger {
 
 // Adds a field to the log entry, note that you it doesn't log until you call
 // Debug, Print, Info, Warn, Fatal or Panic. It only creates a log entry.
-// Ff you want multiple fields, use `WithFields`.
+// If you want multiple fields, use `WithFields`.
 func (logger *Logger) WithField(key string, value interface{}) *Entry {
 	return NewEntry(logger).WithField(key, value)
 }