fixed typo

Author: xalopp

Sniffs/Formatting/AlphabeticalUseStatementsSniff.php

@@ -84,7 +84,7 @@ public function process(PHP_CodeSniffer_File $phpcsFile, $stackPtr)
 
  if ($this->_lastUseStatement !== '') {
  if (strcmp($this->_lastUseStatement, $currentUseStatement) > 0) {
- $msg = 'USE statements mus be sorted alphabetically';
+ $msg = 'USE statements must be sorted alphabetically';
 
  $phpcsFile->addError($msg, $stackPtr);
  }