BUG: Fix GeoSeries constructor for multi geoms

Because Multi* geometries are iterable, they get expanded when passed into
np.array(). Protect against this by passing in all base geometries as a
single element list. They will not be expanded into their individual
parts.

It actually would crash on a `MultiPoint`.

This would happen before:
```
In [3]: df = gpd.read_file('/nybb_13a/nybb.shp', vfs='zip://examples/nybb_13a.zip')

In [4]: multipoly = df.iloc[0].geometry

In [5]: type(multipoly)
Out[5]: shapely.geometry.multipolygon.MultiPolygon

In [6]: gs = gpd.GeoSeries(multipoly)

In [7]: gs
Out[7]:
0    POLYGON ((970217.0223999023437500 145643.33221...
1    POLYGON ((969488.1658325195312500 149753.59460...
2    POLYGON ((939997.0946044921875000 173013.57940...
3    POLYGON ((961436.3049926757812500 175473.02960...
dtype: object
```

Here's the output with this patch:
```
In [2]: df = gpd.read_file('/nybb_13a/nybb.shp', vfs='zip://examples/nybb_13a.zip')

In [3]: multipoly = df.iloc[0].geometry

In [4]: type(multipoly)
Out[4]: shapely.geometry.multipolygon.MultiPolygon

In [5]: gs = gpd.GeoSeries(multipoly)

In [6]: gs
Out[6]:
0    (POLYGON ((970217.0223999023437500 145643.3322...
dtype: object
```