Increase the attempts for thunks to be GC'd during precompilation

This may help fix CI with the DTables.jl test.

Author: JamesWrigley

Diff for: src/precompile.jl

@@ -12,7 +12,7 @@
     # Clean up refs
     t1 = nothing; t2 = nothing
     state = Sch.EAGER_STATE[]
-    for i in 1:5
+    for i in 1:10
         length(state.thunk_dict) == 1 && break
         GC.gc()
         yield()