Raise required compiler to rust 1.39

This is required for attributes on function parameters, which I hope to
use for #[track_caller] / Location support:

    unsafe fn construct<E>(
        error: E,
        vtable: &'static ErrorVTable,
        backtrace: Option<Backtrace>,
        #[cfg(track_caller)] location: &'static Location<'static>,
    ) -> Self
    where
        E: StdError + Send + Sync + 'static;

.github/workflows/ci.yml

@@ -35,7 +35,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.52.0, 1.51.0, 1.50.0, 1.42.0, 1.38.0]
+        rust: [1.52.0, 1.51.0, 1.50.0, 1.42.0, 1.39.0]
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
@@ -45,7 +45,7 @@ jobs:
       - run: cargo check
       - run: cargo check --no-default-features
       - run: cargo check --features backtrace
-        if: matrix.rust != '1.38.0'
+        if: matrix.rust != '1.39.0'
 
   windows:
     name: Windows

Cargo.toml

@@ -9,7 +9,7 @@ edition = "2018"
 keywords = ["error", "error-handling"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/anyhow"
-rust-version = "1.38"
+rust-version = "1.39"
 
 [features]
 default = ["std"]

README.md

@@ -16,7 +16,7 @@ for easy idiomatic error handling in Rust applications.
 anyhow = "1.0"
 ```
 
-*Compiler support: requires rustc 1.38+*
+*Compiler support: requires rustc 1.39+*
 
 <br>