fix broken links in the Cargo book (rust-lang#15109)

This PR closes rust-lang#15102. I fixed broken links in the SUMMARY.md and
guide/index.md of the Cargo book.

Author: ehuss

src/doc/src/guide/build-cache.md

@@ -11,5 +11,5 @@ develop Rust packages.
 * [Cargo.toml vs Cargo.lock](cargo-toml-vs-cargo-lock.md)
 * [Tests](tests.md)
 * [Continuous Integration](continuous-integration.md)
+* [Publishing on crates.io](../reference/publishing.md)
 * [Cargo Home](cargo-home.md)
-* [Build Cache](build-cache.md)

src/doc/src/guide/index.md

@@ -2,29 +2,30 @@
 
 The reference covers the details of various areas of Cargo.
 
-* [Specifying Dependencies](specifying-dependencies.md)
-    * [Overriding Dependencies](overriding-dependencies.md)
 * [The Manifest Format](manifest.md)
     * [Cargo Targets](cargo-targets.md)
+    * [Rust version](rust-version.md)
 * [Workspaces](workspaces.md)
+* [Specifying Dependencies](specifying-dependencies.md)
+    * [Overriding Dependencies](overriding-dependencies.md)
+    * [Source Replacement](source-replacement.md)
+    * [Dependency Resolution](resolver.md)
 * [Features](features.md)
     * [Features Examples](features-examples.md)
 * [Profiles](profiles.md)
 * [Configuration](config.md)
 * [Environment Variables](environment-variables.md)
 * [Build Scripts](build-scripts.md)
     * [Build Script Examples](build-script-examples.md)
-* [Publishing on crates.io](publishing.md)
+* [Build Cache](build-cache.md)
 * [Package ID Specifications](pkgid-spec.md)
-* [Source Replacement](source-replacement.md)
 * [External Tools](external-tools.md)
 * [Registries](registries.md)
     * [Registry Authentication](registry-authentication.md)
         * [Credential Provider Protocol](credential-provider-protocol.md)
     * [Running a Registry](running-a-registry.md)
-        * [Registry Index](registry-index.md)   
-        * [Registry Web API](registry-web-api.md) 
-* [Dependency Resolution](resolver.md)
+        * [Registry Index](registry-index.md)
+        * [Registry Web API](registry-web-api.md)
 * [SemVer Compatibility](semver.md)
 * [Future incompat report](future-incompat-report.md)
 * [Reporting build timings](timings.md)