Buffering line with flat cap style using GeoPandas?

I’m interested in buffering a linestring geometry using a flat cap style rather than the default round cap style using GeoPandas. I see shapely, which geopandas is based off, has the option to do that:

object.buffer(distance, resolution=16, cap_style=2, join_style=1, mitre_limit=1.0)

However, when I try to integrate the cap style into my geopandas script

import geopandas as gp

shp = r'X:templine_shapefile.shp'
outshp =r'X:tempbuffered_line_shapefile.shp'

df = gp.GeoDataFrame.from_file(shp)
buffer = df.buffer(100, cap_style=2)

buffer.to_file(outshp)

it throws an error

Traceback (most recent call last):

  File "<ipython-input-12-9660d1a63146>", line 7, in <module>
    buffer = df.buffer(100, cap_style=2)

TypeError: buffer() got an unexpected keyword argument 'cap_style'

What is the correct implimentation of the flat cap style buffer in GeoPandas?

# Assumes that geometry will be the geometry column
capped_lines = df.geometry.apply(lambda g: g.buffer(100, cap_style=2))

gdf.geometry.to_crs("epsg:3857").buffer(10, cap_style=2)