Backport a patch from upstream to fix the build on HEAD (clang 5).

src/uri/uri.cpp:25:73: error: lambda capture 'this' is not used [-Werror,-Wunused-lambda-capture]

std::transform(m_scheme.begin(), m_scheme.end(), m_scheme.begin(), [this](utility::char_t c) {

src/uri/uri.cpp:30:67: error: lambda capture 'this' is not used [-Werror,-Wunused-lambda-capture]

std::transform(m_host.begin(), m_host.end(), m_host.begin(), [this](utility::char_t c) {