fix an issue with validation error formatting

Author: jescalan

lib/WebpackOptionsValidationError.js

@@ -51,15 +51,16 @@ class WebpackOptionsValidationError extends Error {
 	constructor(validationErrors) {
 		super();
 
-		if(Error.hasOwnProperty("captureStackTrace")) {
-			Error.captureStackTrace(this, this.constructor);
-		}
 		this.name = "WebpackOptionsValidationError";
 
 		this.message = "Invalid configuration object. " +
 			"Webpack has been initialised using a configuration object that does not match the API schema.\n" +
 			validationErrors.map(err => " - " + indent(WebpackOptionsValidationError.formatValidationError(err), "   ", false)).join("\n");
 		this.validationErrors = validationErrors;
+
+		if(Error.hasOwnProperty("captureStackTrace")) {
+			Error.captureStackTrace(this, this.constructor);
+		}
 	}
 
 	static formatSchema(schema, prevSchemas) {