Add .env to .gitignore (IBM-Cloud#6395)

At least in PowerVS, the .env is where we set out environment variables
to test. Although it is located in .vscode directory, which is already
ignored, this will add an additional layer of protection against
accidentally leaking credentials.

Author: ismirlia

.gitignore

@@ -26,6 +26,7 @@ website/node_modules
 *.test
 *.iml
 .vscode
+.env
 website/vendor
 *.attach
 *.xml