Replace Xref ec with 4.2.3.75 for GO term GO:0052577

[rozaru]

For GO:0052577 germacrene-D synthase activity, the current EC number needs to be replaced with ec 4.2.3.75. All the other X-ref are correct.

[sjm41]

I changed the term and def xref to 4.2.3.75 (exactMatch).
But I kept EC:4.2.3.22 as a broadMatch term xref because that EC entry says "Also catalyzes the reaction of EC 4.2.3.75"