tweak compat fix

Author: mlubin

REQUIRE

@@ -1,2 +1,2 @@
 julia 0.3.7
-Compat
+Compat 0.4.0

src/differentiate.jl

@@ -195,11 +195,7 @@ export symbolic_derivatives_1arg
 
 # deprecated: for backward compatibility with packages that used
 # this unexported interface.
-if VERSION < v"0.4.0-dev+4319"
-    derivative_rules = Array((Symbol,Expr),0)
-else
-    derivative_rules = Array(Tuple{Symbol,Expr},0)
-end
+derivative_rules = Array(@Compat.compat(Tuple{Symbol,Expr}),0)
 for (s,ex) in symbolic_derivative_1arg_list
     push!(derivative_rules, (s, :(xp*$ex)))
 end