force output width/height

[vincentsarago]

ref: rasterio/rasterio#1951

When not doing reprojection we can still force output size by doing

vrt_params = dict(add_alpha=True, dtype=dtype, width=src_dst.width, height=src_dst.height) here

rio-cogeo/rio_cogeo/cogeo.py

Line 162 in 3695096

vrt_params = dict(add_alpha=True, dtype=dtype)

cc @kylebarron