doc: use "Long Term Support" in technical values doc

Use "Long Term Support" rather than "long term support".

Refs: nodejs#38839 (comment)

Author: Trott

doc/guides/technical-values.md

@@ -43,7 +43,7 @@ Some key elements of this include:
 * Stable releases on a predictable schedule
 * A strong safety net, including testing how changes
   in Node.js affect popular packages
-* Careful consideration of what goes into long term support (LTS) releases
+* Careful consideration of what goes into Long Term Support (LTS) releases
 
 ### 3 - Operational qualities
 We value keeping Node.js safe, performant, and lightweight.