feat(ios): adapt build to post bintray world (#309)

Part of https://github.com/ooni/probe/issues/1437

build-ios.bash

@@ -7,3 +7,9 @@ go get -u golang.org/x/mobile/cmd/gomobile
 gomobile init
 output=MOBILE/ios/oonimkall.framework
 gomobile bind -target=ios -o $output -ldflags="-s -w" ./pkg/oonimkall
+release=$(git describe --tags)
+version=$(date -u +%Y.%m.%d-%H%M%S)
+podspecfile=./MOBILE/ios/oonimkall.podspec
+(cd ./MOBILE/ios && rm -f oonimkall.framework.zip && zip -yr oonimkall.framework.zip oonimkall.framework)
+podspectemplate=./MOBILE/template.podspec
+cat $podspectemplate|sed -e "s/@VERSION@/$version/g" -e "s/@RELEASE@/$release/g" > $podspecfile