Use Rust 1.25 to build Docker images.
# When PROXY_SKIP_TESTS is set and not empty, tests are not run. Otherwise, tests are run
# against either unoptimized or optimized proxy code, according to PROXY_UNOPTIMIZED.
-ARG RUST_IMAGE=rust:1.24.0
+ARG RUST_IMAGE=rust:1.25.0
ARG RUNTIME_IMAGE=gcr.io/runconduit/base:2017-10-30.01
## Builds the proxy as incrementally as possible.
