Bump MSRV to 1.58.0

We have to use rust-simplicity's MSRV, which is 1.58.0:
BlockstreamResearch/rust-simplicity@c3b86f5

Author: uncomputable

.github/workflows/rust.yml

@@ -69,7 +69,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        rust: [stable, beta, nightly, 1.48.0]
+        rust: [stable, beta, nightly, 1.58.0]
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v2

README.md

@@ -1,6 +1,6 @@
 ![Build](https://github.com/ElementsProject/elements-miniscript/workflows/Continuous%20integration/badge.svg)
 
-**Minimum Supported Rust Version:** 1.48.0
+**Minimum Supported Rust Version:** 1.58.0
 
 *This crate uses "2018" edition
 
@@ -40,7 +40,7 @@ Enabling the `no-std` feature does not disable `std`. To disable the `std` featu
 To run the benchmarks run `RUSTFLAGS=--cfg=miniscript_bench cargo +nightly bench --all-features`.
 
 ## Minimum Supported Rust Version (MSRV)
-This library should always compile with any combination of features on **Rust 1.48.0**.
+This library should always compile with any combination of features on **Rust 1.58.0**.
 
 
 Some dependencies do not play nicely with our MSRV, if you are running the tests

clippy.toml

@@ -1 +1 @@
-msrv = "1.48.0"
+msrv = "1.58.0"

contrib/test.sh

@@ -7,8 +7,8 @@ FEATURES="compiler serde rand base64"
 cargo --version
 rustc --version
 
-# Pin dependencies required to build with Rust 1.48
-if cargo --version | grep "1\.48"; then
+# Pin dependencies required to build with Rust 1.58
+if cargo --version | grep "1\.58"; then
     cargo update -p quote --precise 1.0.28
     cargo update -p proc-macro2 --precise 1.0.63
     cargo update -p serde_json --precise 1.0.99