docs: update URLs from stainlessapi.com to stainless.com (#2150)

More details at https://www.stainless.com/changelog/stainless-com

Author: stainless-app[bot]

SECURITY.md

@@ -2,9 +2,9 @@
 
 ## Reporting Security Issues
 
-This SDK is generated by [Stainless Software Inc](http://stainlessapi.com). Stainless takes security seriously, and encourages you to report any security vulnerability promptly so that appropriate action can be taken.
+This SDK is generated by [Stainless Software Inc](http://stainless.com). Stainless takes security seriously, and encourages you to report any security vulnerability promptly so that appropriate action can be taken.
 
-To report a security issue, please contact the Stainless team at security@stainlessapi.com.
+To report a security issue, please contact the Stainless team at security@stainless.com.
 
 ## Responsible Disclosure