Only replace environment variables in YAML

Author: rbayliss

lib/optimist-config-file.js

@@ -31,12 +31,12 @@ function parseConfigFile(configFileName, replacementVars) {
 	// parse it
 	try {
 		raw = fs.readFileSync(configFileName).toString();
-		if (replacementVars instanceof Object) {
-			raw = replace(raw, replacementVars);
-		}
 
 		switch (configMode) {
 			case 'YAML':
+				if (replacementVars instanceof Object) {
+					raw = replace(raw, replacementVars);
+				}
 				configParsed = yaml.safeLoad(raw);
 				break;