Raise MSRV to 1.40.0 to use non_exhaustive

Author: MathiasKoch

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ name: Continuous integration
 
 env:
   RUSTFLAGS: '--deny warnings'
-  
+
 jobs:
   ci-linux:
     runs-on: ubuntu-latest
@@ -21,7 +21,7 @@ jobs:
 
         include:
           # Test MSRV
-          - rust: 1.36.0
+          - rust: 1.40.0
             TARGET: x86_64-unknown-linux-gnu
 
           # Test nightly but don't fail