Use rbs HEAD for https://github.com/ruby/rbs/pull/1090

gems/bundled_gems

@@ -11,6 +11,6 @@ net-pop         0.1.1   https://github.com/ruby/net-pop
 net-smtp        0.3.1   https://github.com/ruby/net-smtp
 matrix          0.4.2   https://github.com/ruby/matrix
 prime           0.1.2   https://github.com/ruby/prime
-rbs             2.6.0   https://github.com/ruby/rbs             5202d4eeed3257448f19004b4baac4bcf4127717
+rbs             2.6.0   https://github.com/ruby/rbs             5ec9d53efe4bf0a97f33c3016aed430be135583a
 typeprof        0.21.3  https://github.com/ruby/typeprof
 debug           1.6.2   https://github.com/ruby/debug           e7c37486ff9579251e5d25645b8d38ec96708f12