Fix Kingfisher build by the new scheme settings

[onevcat]

This is a fix for #527

It now succeeds as below:

--- Executing build actions ---
$ /Users/onevcat/Desktop/swift-source-compat-suite/runner.py --swift-branch swift-5.1-branch --swiftc /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc --projects /Users/onevcat/Desktop/swift-source-compat-suite/projects.json --include-repos 'path == "Kingfisher"' --include-versions 'version == "5.1"' --include-actions 'action.startswith("Build")'
$ git -C /Users/onevcat/Desktop/swift-source-compat-suite/project_cache/Kingfisher rev-parse --show-toplevel
PASS: Kingfisher, 5.1, 44450a, Kingfisher, generic/platform=iOS
$ git -C /Users/onevcat/Desktop/swift-source-compat-suite/project_cache/Kingfisher rev-parse --show-toplevel
PASS: Kingfisher, 5.1, 44450a, Kingfisher, generic/platform=macOS
$ git -C /Users/onevcat/Desktop/swift-source-compat-suite/project_cache/Kingfisher rev-parse --show-toplevel
PASS: Kingfisher, 5.1, 44450a, Kingfisher, generic/platform=tvOS
$ git -C /Users/onevcat/Desktop/swift-source-compat-suite/project_cache/Kingfisher rev-parse --show-toplevel
PASS: Kingfisher, 5.1, 44450a, Kingfisher, generic/platform=watchOS
========================================
Action Summary:
     Passed: 4
     Failed: 0
    XFailed: 0
    UPassed: 0
      Total: 4
========================================
Repository Summary:
      Total: 1
========================================
Result: PASS
========================================
--- Kingfisher checked successfully against Swift 5.1 ---

[shahmishal]

@swift-ci test