build(fix): Remove unnecessary files from the exported archive (#800)

Author: theofidry

.gitattributes

@@ -8,6 +8,13 @@
 /.styleci.yml                    export-ignore
 /.travis.yml                     export-ignore
 /.appveyor.yml                   export-ignore
+/.github/                        export-ignore
+/_specs/                         export-ignore
+/build/                          export-ignore
+/composer-root-version-checker/  export-ignore
+/docs/                           export-ignore
+/fixtures/                       export-ignore
+/specs/                          export-ignore
+/tests/                          export-ignore
+/vendor-bin/                     export-ignore
 /phpunit.xml.dist                export-ignore
-/composer-root-version-checker   export-ignore
-/tests                           export-ignore