Ignore goto-binary files in the regressions folder

.gb is the standard extension for goto binaries generated by goto-cc and
shouldn't be checked

Author: thk123

.gitignore

@@ -29,6 +29,7 @@ regression/ansi-c/tests.log
 regression/symex/tests.log
 regression/cbmc-java/tests.log
 regression/cbmc/tests.log
+regression/**/*.gb
 src/big-int/test-bigint
 src/big-int/test-bigint.exe