update ABI to match release/v1.15 branch of envoyproxy/envoy-wasm#18

yskopets merged 2 commits intoproxy-wasm-spec-0.1.0yskopets/proxy-wasm-rust-sdk:proxy-wasm-spec-0.1.0from

feature/envoy-1.15yskopets/proxy-wasm-rust-sdk:feature/envoy-1.15Copy head branch name to clipboard