npm install --save @ionic-native/admob-free

+-- @ionic-native/admob-free@4.5.2
`-- UNMET PEER DEPENDENCY @ionic-native/core@4.4.0

npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@^1.0.0 (node_moduleschokidarnode_modulesfsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.1.3: wanted {"os":"darwin","arch":"any"} (current: {"os":"win32","arch":"x64"})
npm WARN @ionic-native/admob@3.14.0 requires a peer of @ionic-native/core@^3.6.0 but none was installed.