安装ReactiveCocoa一直提示下面SWIFT_VERSI

ZHENdeiMac:ReactiveCocoaFromJoseph zhenwang$ pod install
Analyzing dependencies
Downloading dependencies
Using Reachability (3.2)
Installing ReactiveCocoa (9.0.0)
Installing ReactiveSwift (5.0.1)
Installing Result (4.1.0)
[!] Unable to determine Swift version for the following pods:

- `ReactiveCocoa` does not specify a Swift version and none of the targets (`ReactiveCocoaFromJoseph`) integrating it have the `SWIFT_VERSION` attribute set. Please contact the author or set the `SWIFT_VERSION` attribute in at least one of the targets that integrate this pod.

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