Add slack token

Add Slack token from https://api.slack.com/docs/token-types 

#hactoberfest #greywizard

gitleaks.toml

@@ -20,6 +20,9 @@ regex = '''(?i)facebook.*['\"][0-9a-f]{32}['\"]'''
 [[regexes]]
 description = "Twitter"
 regex = '''(?i)twitter.*['\"][0-9a-zA-Z]{35,44}['\"]'''
+[[regexes]]
+description = "Slack token"
+regex = '''xoxo[bapr]-.*'''
 
 [whitelist]
 regexes = [