Change minimum requirement to Julia 0.7 and above

Checks fail for merging into METADATA, probably have to change also the minimal requirements to 0.7 up to 2.0. I copied this line from QuantEcon.jl. I am not sure if another formulation is preferable.
QuantEcon · Sep 28, 2018 · 1c40312 · 1c40312
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commit 1c40312
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/REQUIRE b/REQUIRE
@@ -1,4 +1,4 @@
-julia 0.5
+julia 0.7 2
 QuantEcon
 BasisMatrices 0.3
 Reexport