editorconfig: Adjust to 2-space indents for yaml.

This matches the current configuration in zulip/zulip.

.editorconfig

@@ -10,11 +10,11 @@ charset = utf-8
 trim_trailing_whitespace = true
 insert_final_newline = true
 
-[*.{sh,py,pyi,js,json,yml,xml,css,md,markdown,handlebars,html}]
+[*.{sh,py,pyi,js,json,xml,css,md,markdown,handlebars,html}]
 indent_style = space
 indent_size = 4
 
-[*.{svg,rb,pp,pl}]
+[*.{svg,rb,pp,pl,yaml,yml}]
 indent_style = space
 indent_size = 2