use equals, not equals_exact
use equals, not equals_exact

equals_exact make libgeos 3.6 crash. I don't understand why.

since equals and equals_exact [are
equivalent](https://github.com/libgeos/geos/blob/master/capi/geos_c.h.in#L1746-L1748)
for us (we don't care about types) and used only for test, I don't have
the motivation to dig further.

mthh/rust-geos