bump MSRV to 1.48

windows-sys has a MSRV of 1.48, which forces us to bump the MSRV
of this crate.

Author: vthib

.github/workflows/libloading.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust_toolchain: [nightly, stable, 1.40.0]
+        rust_toolchain: [nightly, stable, 1.48.0]
         os: [ubuntu-latest, windows-latest, macOS-latest]
     timeout-minutes: 20
     steps:

Cargo.toml

@@ -12,7 +12,7 @@ readme = "README.mkd"
 description = "Bindings around the platform's dynamic library loading primitives with greatly improved memory safety."
 keywords = ["dlopen", "load", "shared", "dylib"]
 categories = ["api-bindings"]
-rust-version = "1.40.0"
+rust-version = "1.48.0"
 
 [target.'cfg(windows)'.dependencies.windows-sys]
 version = "0.48"