Bump mcp from 0.18.0 to 0.20.0 in /docs (#424)

Bumps [mcp](https://github.com/modelcontextprotocol/ruby-sdk) from 0.18.0 to 0.20.0.
- [Release notes](https://github.com/modelcontextprotocol/ruby-sdk/releases)
- [Changelog](https://github.com/modelcontextprotocol/ruby-sdk/blob/main/CHANGELOG.md)
- [Commits](modelcontextprotocol/ruby-sdk@v0.18.0...v0.20.0)

---
updated-dependencies:
- dependency-name: mcp
  dependency-version: 0.20.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/Gemfile.lock

@@ -136,6 +136,7 @@ GEM
     erubi (1.13.1)
     globalid (1.3.0)
       activesupport (>= 6.1)
+    hana (1.3.7)
     i18n (1.14.8)
       concurrent-ruby (~> 1.0)
     io-console (0.8.2)
@@ -147,9 +148,11 @@ GEM
     jsbundling-rails (1.3.1)
       railties (>= 6.0.0)
     json (2.19.9)
-    json-schema (6.2.0)
-      addressable (~> 2.8)
-      bigdecimal (>= 3.1, < 5)
+    json_schemer (2.5.0)
+      bigdecimal
+      hana (~> 1.3)
+      regexp_parser (~> 2.0)
+      simpleidn (~> 0.2)
     language_server-protocol (3.17.0.5)
     lint_roller (1.1.0)
     logger (1.7.0)
@@ -166,8 +169,8 @@ GEM
       net-smtp
     marcel (1.1.0)
     matrix (0.4.2)
-    mcp (0.18.0)
-      json-schema (>= 4.1)
+    mcp (0.20.0)
+      json_schemer (>= 2.4)
     method_source (1.1.0)
     mini_mime (1.1.5)
     mini_portile2 (2.8.9)
@@ -296,6 +299,7 @@ GEM
       rexml (~> 3.2, >= 3.2.5)
       rubyzip (>= 1.2.2, < 4.0)
       websocket (~> 1.0)
+    simpleidn (0.2.3)
     sin_lru_redux (2.5.2)
     sqlite3 (2.9.4)
       mini_portile2 (~> 2.8.0)