Bump fastly from 1.13.2 to 1.15.0 (#466)

Bumps [fastly](https://github.com/fastly/fastly-ruby) from 1.13.2 to 1.15.0.
- [Release notes](https://github.com/fastly/fastly-ruby/releases)
- [Changelog](https://github.com/fastly/fastly-ruby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/fastly/fastly-ruby/compare/v1.13.2...v1.15.0)

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

Gemfile

@@ -38,7 +38,7 @@ gem "devise", "~> 4.4"
 gem "draper", "~> 3.0"
 gem "email_validator", "~> 1.6"
 gem "envied", "~> 0.9"
-gem "fastly", "~> 1.13"
+gem "fastly", "~> 1.15"
 gem "fastly-rails", "~> 0.8"
 gem "feedjira", "~> 2.1"
 gem "figaro", "~> 1.1"

Gemfile.lock

@@ -277,7 +277,7 @@ GEM
     faraday_middleware (0.12.2)
       faraday (>= 0.7.4, < 1.0)
     fastimage (2.1.1)
-    fastly (1.13.2)
+    fastly (1.15.0)
     fastly-rails (0.8.0)
       fastly (~> 1.6)
       railties (> 2, < 6)
@@ -951,7 +951,7 @@ DEPENDENCIES
   factory_bot_rails (~> 4.11)
   fake_stripe (~> 0.1)
   faker!
-  fastly (~> 1.13)
+  fastly (~> 1.15)
   fastly-rails (~> 0.8)
   feedjira (~> 2.1)
   figaro (~> 1.1)