Core - update version introduced for current_random_source

Since it appears the next release of Sonic Pi will be a minor version rather
than a patch version, the version number indicating when `current_random_source`
was introduced has been updated.

Author: ethancrawford

app/server/ruby/lib/sonicpi/lang/core.rb

@@ -3875,7 +3875,7 @@ def current_random_source
         SonicPi::Core::SPRand.get_random_number_distribution
       end
       doc name:          :current_random_source,
-          introduced:    Version.new(3,3,2),
+          introduced:    Version.new(3,4,0),
           summary:       "Get current random source",
           doc:           "Returns the source of the current random number generator (what kind of noise is generating the random numbers).