use nix shell for running fastlane ios clean

[jakubgs]

This is a fix that uses Nix to resolve issues for the CI job that cleans up inactive TestFlight users:
https://ci.status.im/job/status-tools/job/clean-testflight-users

[status-github-bot]

Pull Request Checklist

• Have you updated the documentation, if impacted (e.g. docs.status.im)?

[status-im-auto]

Jenkins Builds

Click to see older builds (23)

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	f175990	#1	2019-06-13 05:32:10	~11 min	linux	📦 App
✔️	f175990	#1	2019-06-13 05:33:18	~12 min	macos	📦 dmg
✔️	f175990	#1	2019-06-13 05:33:40	~13 min	ios	📦 ipa
✔️	f175990	#1	2019-06-13 05:34:08	~13 min	android	📦 apk
✔️	f175990	#1	2019-06-13 05:34:21	~13 min	android-e2e	📦 apk
✔️	f175990	#1	2019-06-13 05:35:34	~14 min	windows	📦 exe
✔️	7f64f80	#2	2019-06-13 15:27:47	~11 min	windows	📦 exe
✔️	7f64f80	#2	2019-06-13 15:28:36	~12 min	linux	📦 App
✔️	7f64f80	#2	2019-06-13 15:29:17	~13 min	ios	📦 ipa
✔️	7f64f80	#2	2019-06-13 15:29:25	~13 min	android	📦 apk
✔️	7f64f80	#2	2019-06-13 15:29:41	~13 min	android-e2e	📦 apk
✔️	7f64f80	#2	2019-06-13 15:31:21	~15 min	macos	📦 dmg
✔️	658e5ca	#3	2019-06-14 12:55:26	~11 min	ios	📦 ipa
✔️	658e5ca	#3	2019-06-14 12:56:59	~13 min	android	📦 apk
✔️	658e5ca	#3	2019-06-14 12:57:15	~13 min	android-e2e	📦 apk
✔️	658e5ca	#3	2019-06-14 12:58:54	~15 min	macos	📦 dmg
✔️	658e5ca	#3	2019-06-14 12:59:25	~15 min	linux	📦 App
✔️	658e5ca	#3	2019-06-14 12:59:52	~16 min	windows	📦 exe
✔️	f88c79b	#7	2019-06-14 15:43:02	~11 min	ios	📦 ipa
✔️	f88c79b	#7	2019-06-14 15:44:37	~13 min	android	📦 apk
✔️	f88c79b	#7	2019-06-14 15:44:46	~13 min	android-e2e	📦 apk
✔️	f88c79b	#7	2019-06-14 15:47:05	~15 min	macos	📦 dmg
✔️	f88c79b	#7	2019-06-14 15:47:40	~16 min	linux	📦 App

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	0561d13	#8	2019-06-14 16:00:32	~13 min	ios	📦 ipa
✔️	0561d13	#8	2019-06-14 16:01:21	~13 min	macos	📦 dmg
✔️	0561d13	#8	2019-06-14 16:01:53	~14 min	windows	📦 exe
✔️	0561d13	#8	2019-06-14 16:02:51	~15 min	linux	📦 App
✔️	0561d13	#8	2019-06-14 16:03:45	~16 min	android	📦 apk
✔️	0561d13	#8	2019-06-14 16:03:59	~16 min	android-e2e	📦 apk
❌	13d8493	#9	2019-06-14 18:19:00	~3 min	linux	📄 log
✔️	13d8493	#9	2019-06-14 18:26:18	~10 min	ios	📦 ipa
✔️	13d8493	#9	2019-06-14 18:28:31	~12 min	macos	📦 dmg
✔️	13d8493	#9	2019-06-14 18:29:02	~13 min	android	📦 apk
✔️	13d8493	#9	2019-06-14 18:29:18	~13 min	android-e2e	📦 apk
✔️	13d8493	#9	2019-06-14 18:29:21	~13 min	windows	📦 exe

[jakubgs]

I want to merge this, but It tested this fix, and while it does solve the failure to run Fastlane, it still fails to actually remove any users, for example:

22:03:18  [03:03:18]: Login to iTunes Connect (****)
22:03:20  [03:03:20]: Login successful
22:03:20  [03:03:20]: Fetching all TestFlight testers, this might take a few minutes, depending on the number of testers
22:16:46  [03:16:36]: Removing tester dylanjohnlukes@gmail.com due to inactivity from app ID 1178893006...
...(omitted FAILURE with bunch of HTML)...

https://ci.status.im/job/status-tools/job/clean-testflight-users/515/

I've opened an issue with the plugin but I doubt we're gonna get anywhere with that:
fastlane-community/fastlane-plugin-clean_testflight_testers#10

For now I'm going to merge this and research the new issue separately.