Actualize the content of the .gitattributes file

1. Removed no longer existing entries
2. Added new entries
3. Sorted using `sort` (ignores case and the leading dot, same as `ls`)

.gitattributes

 /.appveyor.yml export-ignore
+/composer.lock export-ignore
+/docs export-ignore
+/.doctrine-project.json export-ignore
 /.gitattributes export-ignore
 /.github export-ignore
 /.gitignore export-ignore
-/.scrutinizer.yml export-ignore
-/.travis.yml export-ignore
-/build.properties export-ignore
-/build.xml export-ignore
-/composer.lock export-ignore
-/docs export-ignore
 /phpcs.xml.dist export-ignore
 /phpstan.neon.dist export-ignore
 /phpunit.xml.dist export-ignore
 /run-all.sh export-ignore
+/.scrutinizer.yml export-ignore
+/SECURITY.md export-ignore
 /tests export-ignore
+/.travis.yml export-ignore
+/UPGRADE.md export-ignore