Update minimal supported Rust version to 1.41.1

Rustc 1.41.1 is now packaged in Debian and thus a convservative choice
for this libraries minimal suported Rust version.

Author: Thomas Bahn

.github/workflows/ci.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.33.0, stable, beta, nightly]
+        rust: [1.41.1, stable, beta, nightly]
     steps:
       - uses: actions/checkout@v2
       - uses: hecrj/setup-rust-action@v1

.travis.yml

@@ -1,7 +1,7 @@
 language: rust
 cache: cargo
 rust:
-  - 1.33.0
+  - 1.41.1
   - stable
   - beta
   - nightly