Update Coq.gitignore

Add various files that show up when you run tactics (the *.cache in 8.4 and 8.5, .*.cache in 8.6), build plugins (the various OCaml files), and for the native compiler of Coq 8.5.

Coq.gitignore

-*.vo
+.*.aux
+*.a
+*.cma
+*.cmi
+*.cmo
+*.cmx
+*.cmxa
+*.cmxs
 *.glob
+*.ml.d
+*.ml4.d
+*.mli.d
+*.o
 *.v.d
+*.vio
+*.vo
+.coq-native/
+.csdp.cache
+.lia.cache
+.nia.cache
+.nlia.cache
+.nra.cache
+csdp.cache
+lia.cache
+nia.cache
+nlia.cache
+nra.cache