Bump fastimage from 2.1.5 to 2.1.7 (#11785)

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

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

Gemfile.lock

@@ -236,7 +236,7 @@ GEM
     faraday (0.15.0)
       multipart-post (>= 1.2, < 3)
     fast_blank (1.0.0)
-    fastimage (2.1.5)
+    fastimage (2.1.7)
     ffi (1.10.0)
     fog-core (2.1.0)
       builder