Timeseries.copy() leaves reference to original channel object

Created by: areeda

Code to reproduce:

from gwpy.timeseries import TimeSeries

ts = TimeSeries.fetch('L1:PEM-CS_ACC_BSC1_ITMY_X_MON', 1223067348, 1223067349)

ts2 = ts.copy()
ts2.channel.name += '#copy'

print (ts.channel.name)

Produces: L1:PEM-CS_ACC_BSC1_ITMY_X_MON#copy