Replaced "retreive" with "retrieve".

src/Umbraco.Web/WebApi/UmbracoApiController.cs

@@ -33,7 +33,7 @@ namespace Umbraco.Web.WebApi
         private readonly MembershipHelper _membershipHelper;
 
         /// <summary>
-        /// Tries to retreive the current HttpContext if one exists.
+        /// Tries to retrieve the current HttpContext if one exists.
         /// </summary>
         /// <returns></returns>
         protected Attempt<HttpContextBase> TryGetHttpContext()
@@ -97,4 +97,4 @@ namespace Umbraco.Web.WebApi
         internal Guid InstanceId { get; private set; }
 
     }
-}
+}