update hardcoded version references to 1.2.0 (#56)
update hardcoded version references to 1.2.0 (#56)

which I think will be the upcoming release version.
cross-language-cpp/djinni-support-lib,cross-language-cpp/djinni-support-lib,cross-language-cpp/djinni-support-lib,cross-language-cpp/djinni-support-lib,cross-language-cpp/djinni-support-lib