diff --git a/lib/adapters/xhr.js b/lib/adapters/xhr.js
index 078a9db..c90b9f8 100644
--- a/lib/adapters/xhr.js
+++ b/lib/adapters/xhr.js
@@ -19,7 +19,7 @@ module.exports = function xhrAdapter(resolve, reject, config) {
 
   // For IE 8/9 CORS support
   // Only supports POST and GET calls and doesn't returns the response headers.
-  if (window.XDomainRequest && !("withCredentials" in request) && !isURLSameOrigin(config.url)) {
+  if (window.XDomainRequest && !('withCredentials' in request) && !isURLSameOrigin(config.url)) {
     request = new window.XDomainRequest();
   }
 
@@ -41,7 +41,7 @@ module.exports = function xhrAdapter(resolve, reject, config) {
       return;
     }
     // Prepare the response
-    var responseHeaders = "getAllResponseHeaders" in request ? parseHeaders(request.getAllResponseHeaders()) : null;
+    var responseHeaders = 'getAllResponseHeaders' in request ? parseHeaders(request.getAllResponseHeaders()) : null;
     var responseData = ['text', ''].indexOf(config.responseType || '') !== -1 ? request.responseText : request.response;
     var response = {
       data: transformData(
@@ -55,7 +55,7 @@ module.exports = function xhrAdapter(resolve, reject, config) {
       config: config
     };
     // Resolve or reject the Promise based on the status
-    ((request.status >= 200 && request.status < 300) || (!("status" in request) && request.responseText) ?
+    ((request.status >= 200 && request.status < 300) || (!('status' in request) && request.responseText) ?
       resolve :
       reject)(response);
 
@@ -80,7 +80,7 @@ module.exports = function xhrAdapter(resolve, reject, config) {
   }
 
   // Add headers to the request
-  if ("setRequestHeader" in request) {
+  if ('setRequestHeader' in request) {
     utils.forEach(requestHeaders, function setRequestHeader(val, key) {
       if (!requestData && key.toLowerCase() === 'content-type') {
         // Remove Content-Type if data is undefined