Update `isRunningOnDevice` to use `targetEnvironment(simulator)`. Update `.swift-version` to 4.1.

.swift-version

@@ -1 +1 @@
-4
+4.1

Reachability/Reachability.swift

@@ -133,7 +133,7 @@ public class Reachability {
     fileprivate var previousFlags: SCNetworkReachabilityFlags?
     
     fileprivate var isRunningOnDevice: Bool = {
-        #if (arch(i386) || arch(x86_64)) && os(iOS)
+        #if targetEnvironment(simulator)
             return false
         #else
             return true