Update do_shortcode sniff

Author: dingo-d

Infinum/Sniffs/Shortcodes/DisallowDoShortcodeSniff.php

@@ -37,7 +37,7 @@ public function process( PHP_CodeSniffer_File $phpcsFile, $stackPtr ) {
     $tokens = $phpcsFile->getTokens();
     $token  = $tokens[ $stackPtr ];
 
-    if ( preg_match( '`do_shortcode`im', $token['content'] ) > 0 ) {
+    if ( preg_match( '`^do_shortcode`i', $token['content'] ) > 0 ) {
       $phpcsFile->addWarning( 'Do not include do_shortcode() function in theme files. Use shortcode callback function instead.' , $stackPtr, 'do_shortcodeDetected' );
     }
   }