fix node_modules permissions before git clean

[jakubgs]

This is due to copying node_modules from nix store which is read-only.
Should fix Nightly build errors like this:

22:59:43  + make clean
22:59:43  git clean -dxf -f
22:59:44  warning: failed to remove node_modules/is-plain-obj/license: Permission denied
22:59:44  warning: failed to remove node_modules/is-plain-obj/index.js: Permission denied
22:59:44  warning: failed to remove node_modules/is-plain-obj/readme.md: Permission denied
22:59:44  warning: failed to remove node_modules/is-plain-obj/package.json: Permission denied
22:59:44  warning: failed to remove node_modules/plist/LICENSE: Permission denied
...

https://ci.status.im/job/status-react/job/nightly/1114/

[status-github-bot]

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❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
❌	401bb33	#1	2019-06-13 13:42:54	~15 sec	android-e2e	📄 log
❌	401bb33	#1	2019-06-13 13:43:10	~29 sec	android	📄 log
❌	401bb33	#1	2019-06-13 13:43:26	~41 sec	windows	📄 log
❌	401bb33	#1	2019-06-13 13:43:27	~44 sec	linux	📄 log
❌	401bb33	#1	2019-06-13 13:44:15	~1 min	ios	📄 log
❌	401bb33	#1	2019-06-13 13:44:31	~1 min	macos	📄 log

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	74b27aa	#2	2019-06-13 13:59:25	~12 min	android-e2e	📦 apk
✔️	74b27aa	#2	2019-06-13 14:01:21	~14 min	ios	📦 ipa
✔️	74b27aa	#2	2019-06-13 14:02:03	~14 min	android	📦 apk
✔️	74b27aa	#2	2019-06-13 14:04:42	~17 min	linux	📦 App
✔️	74b27aa	#2	2019-06-13 14:06:12	~18 min	macos	📦 dmg
✔️	74b27aa	#2	2019-06-13 14:08:17	~20 min	windows	📦 exe
✔️	1a4763c	#3	2019-06-13 14:46:39	~24 min	android-e2e	📦 apk