Use echo -n rather than echo to avoid trailing newline...

...during secret creation

docs/user-guide/kubectl-cheatsheet.md

@@ -90,8 +90,8 @@ metadata:
   name: mysecret
 type: Opaque
 data:
-  password: $(echo "s33msi4" | base64)
-  username: $(echo "jane" | base64)
+  password: $(echo -n "s33msi4" | base64)
+  username: $(echo -n "jane" | base64)
 EOF
 
 ```