Do not export box.sh and benchmark.sh.

.gitattributes

@@ -5,6 +5,8 @@
 .gitignore export-ignore
 .travis.yml export-ignore
 appveyor.yml export-ignore
+benchmark.sh export-ignore
+box.json export-ignore
 phpunit.xml.dist export-ignore
 *       text=auto eol=lf
 *.php   text whitespace=blank-at-eol,blank-at-eof,space-before-tab,tab-in-indent,tabwidth=4 diff=php