Update indexmap dependency used for preserve_order feature to version 2

Author: dtolnay

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [beta, 1.56.1]
+        rust: [beta, 1.64.0, 1.56.1]
         os: [ubuntu]
         include:
           - rust: stable
@@ -61,7 +61,9 @@ jobs:
       - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc,arbitrary_precision
       - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc,raw_value
       - run: cargo check --features preserve_order
+        if: matrix.rust != '1.56.1'
       - run: cargo check --manifest-path tests/crate/Cargo.toml --no-default-features --features alloc,preserve_order
+        if: matrix.rust != '1.56.1'
       - name: Build without std
         run: cargo check --manifest-path tests/crate/Cargo.toml --target ${{matrix.target}} --no-default-features --features alloc
         if: matrix.target

Cargo.toml

@@ -13,7 +13,7 @@ rust-version = "1.36"
 
 [dependencies]
 serde = { version = "1.0.100", default-features = false }
-indexmap = { version = "1.5.2", features = ["std"], optional = true }
+indexmap = { version = "2", optional = true }
 itoa = "1.0"
 ryu = "1.0"