Update custom-proxy.md (Warning Box)

The last sentence is a fragment. "When you enable third-party libraries in device-mode, Segment loads them, which defeats the purpose of self-hosting. Self-hosting Analytics.js requires" 

I've removed the last sentence: 

"Self-hosting Analytics.js requires" As this is a fragment and has not been completed.

Author: PcooperSegment

src/connections/sources/catalog/libraries/website/javascript/custom-proxy.md

@@ -173,4 +173,4 @@ To add a CNAME record to your DNS settings:
 Follow the instructions at [Using Analytics.js as an NPM Package](https://github.com/segmentio/analytics-next/tree/master/packages/browser#-using-as-an-npm-package), to host Analytics.js and eliminate the requirement of downloading it from the CDN file during every page load. This enables you to self-host/import the library itself.
 
 > warning "Keep in mind"
-> Segment does not recommend self-hosting, as it requires that you configure integration settings individually and manually redeploy Analytics.js when there are changes to your settings. When you enable third-party libraries in device-mode, Segment loads them, which defeats the purpose of self-hosting. Self-hosting Analytics.js requires 
+> Segment does not recommend self-hosting, as it requires that you configure integration settings individually and manually redeploy Analytics.js when there are changes to your settings. When you enable third-party libraries in device-mode, Segment loads them, which defeats the purpose of self-hosting.