build(deps-dev): bump solargraph from 0.39.8 to 0.39.12

Bumps [solargraph](https://github.com/castwide/solargraph) from 0.39.8 to 0.39.12.
- [Release notes](https://github.com/castwide/solargraph/releases)
- [Commits](castwide/solargraph@v0.39.8...v0.39.12)

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

Author: dependabot[bot]

Gemfile.lock

@@ -298,11 +298,11 @@ GEM
       mini_portile2 (~> 2.4.0)
     os (1.0.1)
     palm_civet (1.1.0)
-    parallel (1.19.1)
+    parallel (1.19.2)
     parallel_tests (3.0.0)
       parallel
-    parser (2.7.1.3)
-      ast (~> 2.4.0)
+    parser (2.7.1.4)
+      ast (~> 2.4.1)
     pg (1.2.3)
     posix-spawn (0.3.13)
     protobuf (3.6.12)
@@ -429,7 +429,7 @@ GEM
       rack-protection (= 2.0.8.1)
       sinatra (= 2.0.8.1)
       tilt (~> 2.0)
-    solargraph (0.39.8)
+    solargraph (0.39.12)
       backport (~> 1.1)
       benchmark
       bundler (>= 1.17.2)