Add VulnCheck XDB Exploit Database

Also Removed a dead link for OSVDB

Author: patrickmgarrity

README.md

@@ -178,12 +178,12 @@ Table of Contents
    * http://cve.mitre.org/ - Common Vulnerabilities and Exposures. The Standard for Information Security Vulnerability Names
    * https://www.exploit-db.com/ - The Exploit Database – ultimate archive of Exploits, Shellcode, and Security Papers.
    * http://0day.today/ - Inj3ct0r is the ultimate database of exploits and vulnerabilities and a great resource for vulnerability researchers and security professionals.
-   * http://osvdb.org/ - OSVDB's goal is to provide accurate, detailed, current, and unbiased technical security information.
    * http://www.securityfocus.com/ - Since its inception in 1999, SecurityFocus has been a mainstay in the security community.
    * http://packetstormsecurity.com/ - Global Security Resource
    * https://wpvulndb.com/ - WPScan Vulnerability Database
    * https://snyk.io/vuln/ - Vulnerability DB, Detailed information and remediation guidance for known vulnerabilities.
    * https://stellastra.com/cipher-suite - Database of hundreds of TLS cipher suites and their security status.
+   * https://vulncheck.com/xdb/ - An index of exploit proof-of-concept code in Git repositories.
 
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