Bump steep from 1.8.0.pre.2 to 1.8.0 in /steep

Bumps [steep](https://github.com/soutaro/steep) from 1.8.0.pre.2 to 1.8.0.
- [Release notes](https://github.com/soutaro/steep/releases)
- [Changelog](https://github.com/soutaro/steep/blob/master/CHANGELOG.md)
- [Commits](soutaro/steep@v1.8.0.pre.2...v1.8.0)

---
updated-dependencies:
- dependency-name: steep
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

steep/Gemfile

@@ -1,4 +1,4 @@
 source "https://rubygems.org"
 
 gem "rbs", "~> 3.6.0.pre"
-gem "steep", "~> 1.8.0.pre"
+gem "steep", "~> 1.8.0"

steep/Gemfile.lock

@@ -38,10 +38,10 @@ GEM
     rb-fsevent (0.11.2)
     rb-inotify (0.11.1)
       ffi (~> 1.0)
-    rbs (3.6.0.pre.2)
+    rbs (3.6.0)
       logger
     securerandom (0.3.1)
-    steep (1.8.0.pre.2)
+    steep (1.8.0)
       activesupport (>= 5.1)
       concurrent-ruby (>= 1.1.10)
       csv (>= 3.0.9)
@@ -52,7 +52,7 @@ GEM
       logger (>= 1.3.0)
       parser (>= 3.1)
       rainbow (>= 2.2.2, < 4.0)
-      rbs (~> 3.6.0.pre)
+      rbs (~> 3.6.0)
       securerandom (>= 0.1)
       strscan (>= 1.0.0)
       terminal-table (>= 2, < 4)
@@ -68,7 +68,7 @@ PLATFORMS
 
 DEPENDENCIES
   rbs (~> 3.6.0.pre)
-  steep (~> 1.8.0.pre)
+  steep (~> 1.8.0)
 
 BUNDLED WITH
    2.5.16