[ios] Use current Swift version with jazzy

Fixes #4468.

platform/ios/scripts/document.sh

@@ -19,6 +19,8 @@ BRANCH=$( git describe --tags --match=ios-v*.*.* --abbrev=0 )
 SHORT_VERSION=$( echo ${BRANCH} | sed 's/^ios-v//' )
 RELEASE_VERSION=$( echo ${SHORT_VERSION} | sed -e 's/^ios-v//' -e 's/-.*//' )
 
+SWIFT_VERSION=$(xcrun swift -version | head -n 1 | sed -e 's/^Apple Swift version //' -e 's/ .*$//')
+
 rm -rf /tmp/mbgl
 mkdir -p /tmp/mbgl/
 README=/tmp/mbgl/README.md
@@ -32,6 +34,7 @@ mkdir -p ${OUTPUT}
 
 jazzy \
     --sdk iphonesimulator \
+    --swift-version $SWIFT_VERSION \
     --github-file-prefix https://github.com/mapbox/mapbox-gl-native/tree/${BRANCH} \
     --module-version ${SHORT_VERSION} \
     --readme ${README} \