Added extension and ctor for IActionResult

.Net Core brings the IActionResult interface, I've added an extension and a constructor for the IActionResult interface to make the Assertions compatible.

Author: Gimly

src/FluentAssertions.Mvc.Shared/ActionResultAssertions.cs

@@ -29,6 +29,13 @@ public ActionResultAssertions (ActionResult subject) : base(subject)
 			Subject = subject;
 		}
 
+#if NETSTANDARD1_6
+        public ActionResultAssertions (IActionResult subject): base(subject)
+        {
+            Subject = subject;
+        }
+#endif
+
         /// <summary>
         /// Asserts that the subject is a <see cref="ContentResult"/>.
         /// </summary>

src/FluentAssertions.Mvc.Shared/AssertionsExtensions.cs

@@ -27,6 +27,17 @@ public static ActionResultAssertions Should (this ActionResult actual)
             return new ActionResultAssertions (actual);
         }
 
+#if NETSTANDARD1_6
+        /// <summary>
+        /// Returns an <see cref="ActionResultAssertions"/> object that can be used to assert the
+        /// current <see cref="IActionResult"/>.
+        /// </summary>
+        public static ActionResultAssertions Should (this IActionResult actual)
+        {
+            return new ActionResultAssertions (actual);
+        }
+#endif
+
         /// <summary>
         /// Returns an <see cref="RouteDataAssertions"/> object that can be used to assert the
         /// current <see cref="RouteData"/>.