You can use Oskars answer to get the swiftlang version (in your case: 703.0.18).
Now you just have to lookup for the Swift version in the following table:
Swiftlang version Swift version
- -
swiftlang-602.0.49.3 1.2
swiftlang-602.0.49.6 1.2
swiftlang-602.0.53.1 1.2
swiftlang-700.0.59 2.0
swiftlang-700.1.101.6 2.1
swiftlang-700.1.101.15 2.1.1
swiftlang-703.0.18.1 2.2
swiftlang-703.0.18.8 2.2
swiftlang-800.0.46.2 3.0
swiftlang-800.0.58.6 3.0.1
swiftlang-800.0.63 3.0.2
swiftlang-802.0.48 3.1
swiftlang-802.0.51 3.1
swiftlang-802.0.53 3.1
Source: Wikipedia
So 703.0.18 means Swift version 2.2.