Cannot run "pod install" with RN 0.70 or earlier

I'm not sure what the official RN version support policy is, but, as of release 0.3.2, `react-native-masked-view` is no longer compatible with RN 0.70 or earlier (in iOS), due to the `podspec` calling `install_modules_dependencies`, which was added (I believe) in RN 0.71.

Running `pod install` in a project using RN 0.70 results in the following error:

```
[!] Invalid `Podfile` file:
[!] Invalid `RNCMaskedView.podspec` file: undefined method `install_modules_dependencies' for module Pod.

# from /Users/thomasstephens/project/node_modules/@react-native-masked-view/masked-view/RNCMaskedView.podspec:18
# -------------------------------------------
#
> install_modules_dependencies(s)
# end
# -------------------------------------------
.

# from /Users/thomasstephens/project/ios/Podfile:13
# -------------------------------------------
#
> config = use_native_modules!
#
# -------------------------------------------
```

This change was added in #228, although I'm not sure why, since that was an Android-specific change. See https://github.com/react-native-masked-view/masked-view/pull/228/files#diff-fd418d389ed9c48a67ad56f919548e3e5e0801e1a4b00ade786654a231a54eadL18

Version 0.3.1 does not have this issue.