BUG: SparseSeries.abs() resets name
```
# OK: name is preserved
s = pd.Series([1, 2, -3], name='a')
s.abs()
#0    1
#1    2
#2    3
# Name: a, dtype: int64

# NG: name is reset
s = pd.SparseSeries([1, 0, -3], name='a')
s.name
# 'a'

s.abs()
#0    1
#1    0
#2    3
# dtype: int64
# BlockIndex
# Block locations: array([0], dtype=int32)
# Block lengths: array([3], dtype=int32)
```
