Bump MSRV to 1.36.0

Debian is shipping 1.41 on oldstable and rust-bitcoin will likely
move to 1.36 over the coming months, so there's little reason to
wait on this.

cc rust-bitcoin/rust-bitcoin#510

.github/workflows/build.yml

@@ -9,10 +9,10 @@ jobs:
         platform: [ ubuntu-latest ]
         toolchain: [ stable,
                      beta,
-                     # 1.30.0 is MSRV for Rust-Lightning
-                     1.30.0,
+                     # 1.36.0 is MSRV for Rust-Lightning
+                     1.36.0,
                      # 1.34.2 is Debian stable
-                     1.34.2,
+                     1.41.0,
                      # 1.45.2 is MSRV for lightning-net-tokio, lightning-block-sync, and coverage generation
                      1.45.2]
         include:

CONTRIBUTING.md

@@ -75,8 +75,7 @@ be covered by functional tests.
 When refactoring, structure your PR to make it easy to review and don't
 hestitate to split it into multiple small, focused PRs.
 
-The Minimal Supported Rust Version is 1.30.0 (enforced by our Travis and
-GitHub Actions).
+The Minimal Supported Rust Version is 1.36.0 (enforced by our GitHub Actions).
 
 Commits should cover both the issue fixed and the solution's rationale.
 These [guidelines](https://chris.beams.io/posts/git-commit/) should be kept in mind.