Fix landing page heading capitalization

Align with our style guide: use sentence case for headings.

Author: lmktfy

content/en/_index.html

@@ -14,21 +14,21 @@
 {{% /blocks/feature %}}
 
 {{% blocks/feature image="scalable" %}}
-#### Planet Scale
+#### Planet scale
 
 Designed on the same principles that allow Google to run billions of containers a week, Kubernetes can scale without increasing your operations team.
 
 {{% /blocks/feature %}}
 
 {{% blocks/feature image="blocks" %}}
-#### Never Outgrow
+#### Never outgrow
 
 Whether testing locally or running a global enterprise, Kubernetes flexibility grows with you to deliver your applications consistently and easily no matter how complex your need is.
 
 {{% /blocks/feature %}}
 
 {{% blocks/feature image="suitcase" %}}
-#### Run K8s Anywhere
+#### Run K8s anywhere
 
 Kubernetes is open source giving you the freedom to take advantage of on-premises, hybrid, or public cloud infrastructure, letting you effortlessly move workloads to where it matters to you.