Bump RDoc to 1f93543 (rbs-integrated)

With the build infrastructure for bundled-gem C extensions in place,
`rdoc` can be bumped to the rbs-integrated commit. `rdoc-7.2.0`
declares `add_dependency 'rbs', '>= 4.0.0'`, and `rbs` ships a C
extension; the previous commit ensures `rbs` gets built and its
gemspec lands in `.bundle/specifications/` before doc generation
runs, so `require 'rdoc/rdoc'` can transitively activate
`rbs (>= 4.0.0)` through rdoc's runtime dependencies.

Author: st0012

gems/bundled_gems

@@ -37,7 +37,7 @@ ostruct             0.6.3   https://github.com/ruby/ostruct
 pstore              0.2.1   https://github.com/ruby/pstore
 benchmark           0.5.0   https://github.com/ruby/benchmark
 logger              1.7.0   https://github.com/ruby/logger
-rdoc                7.2.0   https://github.com/ruby/rdoc bc0baee787609f2205e8f1103f3e1d36b923184a
+rdoc                7.2.0   https://github.com/ruby/rdoc 1f93543615928b6d45357432f16ec6006e2d8b1e
 win32ole            1.9.3   https://github.com/ruby/win32ole
 irb                 1.18.0  https://github.com/ruby/irb
 reline              0.6.3   https://github.com/ruby/reline