Update configs for Xcode 9.3

[ukitaka]

Waiting for TravisCI to support Xcode 9.3 ...

[codecov-io]

Codecov Report

Merging #9 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master       #9   +/-   ##
=======================================
  Coverage   93.97%   93.97%           
=======================================
  Files          12       12           
  Lines         697      697           
  Branches       30       30           
=======================================
  Hits          655      655           
  Misses         42       42

Impacted Files	Coverage Δ
Sources/AnyRealmIO.swift	95.12% <ø> (ø)	:arrow_up:
Sources/RealmIO.swift	88.23% <ø> (ø)	:arrow_up:
Sources/Realm+Run.swift	92.85% <ø> (ø)	:arrow_up:
Sources/Realm+Util.swift	100% <ø> (ø)	:arrow_up:
Sources/Realm+Operator.swift	97.4% <ø> (ø)	:arrow_up:

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Continue to review full report at Codecov.

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[ukitaka]

Realm's pre-compiled framework seems to be build in swift 4.0.3, and It takes over 10 minute to build realm from source files. Therefore, Travis CI terminates the process...

*** Skipped installing realm-cocoa.framework binary due to the error:
	"Incompatible Swift version - framework was built with 4.0.3 (swiftlang-900.0.74.1 clang-900.0.39.2) and the local version is 4.1 (swiftlang-902.0.48 clang-902.0.37.1)."
*** Checking out realm-cocoa at "v3.3.2"
*** Cloning realm-cocoa
*** xcodebuild output can be found in /var/folders/bb/n7t3rs157850byt_jfdcq9k80000gn/T/carthage-xcodebuild.7M7BfH.log
*** Building scheme "Nimble-iOS" in Nimble.xcodeproj
*** Building scheme "Quick-iOS" in Quick.xcworkspace
*** Building scheme "Realm" in Realm.xcworkspace
No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received
The build has been terminated

Waiting for the new version of realm-cocoa, that precompiled framework built in swift 4.1.