Make project build pass with swift 4.0

- pod update
- Force compile rxcocoa and rxswift with swift 3.2

Pods/RxSwift/RxSwift/Observable.swift

@@ -37,8 +37,8 @@ public class Observable<Element> : ObservableType {
     // Swift compiler reports "Not supported yet" when trying to override protocol extensions, so ¯\_(ツ)_/¯
 
     /// Optimizations for map operator
-    internal func composeMap<R>(_ selector: @escaping (Element) throws -> R) -> Observable<R> {
-        return Map(source: self, transform: selector)
+    internal func composeMap<R>(_ transform: @escaping (Element) throws -> R) -> Observable<R> {
+        return _map(source: self, transform: transform)
     }
 }