[Security] Bump nokogiri from 1.8.4 to 1.9.1 in /src/mobile/android

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.8.4 to 1.9.1. **This update includes security fixes.**
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md)
- [Commits](sparklemotion/nokogiri@v1.8.4...v1.9.1)

Signed-off-by: dependabot[bot] <[email protected]>

src/mobile/android/Gemfile.lock

@@ -64,8 +64,6 @@ GEM
       xcodeproj (>= 1.6.0, < 2.0.0)
       xcpretty (~> 0.3.0)
       xcpretty-travis-formatter (>= 0.0.3)
-    fastlane-plugin-increment_version_code (0.4.3)
-    fastlane-plugin-load_json (0.0.1)
     gh_inspector (1.1.3)
     google-api-client (0.23.9)
       addressable (~> 2.5, >= 2.5.1)
@@ -102,14 +100,14 @@ GEM
       mime-types-data (~> 3.2015)
     mime-types-data (3.2018.0812)
     mini_magick (4.5.1)
-    mini_portile2 (2.3.0)
+    mini_portile2 (2.4.0)
     multi_json (1.13.1)
     multi_xml (0.6.0)
     multipart-post (2.0.0)
     nanaimo (0.2.6)
     naturally (2.2.0)
-    nokogiri (1.8.4)
-      mini_portile2 (~> 2.3.0)
+    nokogiri (1.9.1)
+      mini_portile2 (~> 2.4.0)
     os (1.0.0)
     plist (3.4.0)
     public_suffix (2.0.5)
@@ -159,8 +157,6 @@ PLATFORMS
 
 DEPENDENCIES
   fastlane
-  fastlane-plugin-increment_version_code
-  fastlane-plugin-load_json
   nokogiri
 
 BUNDLED WITH