Bump fastimage from 2.1.5 to 2.1.7

Bumps [fastimage](https://github.com/sdsykes/fastimage) from 2.1.5 to 2.1.7.
- [Release notes](https://github.com/sdsykes/fastimage/releases)
- [Commits](sdsykes/fastimage@v2.1.5...v2.1.7)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Gemfile.lock

@@ -30,7 +30,7 @@ GEM
       thor
     faraday (0.15.4)
       multipart-post (>= 1.2, < 3)
-    fastimage (2.1.5)
+    fastimage (2.1.7)
     hikidoc (0.1.0)
     jasmine (2.99.0)
       jasmine-core (>= 2.99.0, < 3.0.0)