df.eval: "log10" is not a supported function
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd
import numpy as np
df = pd.DataFrame({'a': np.random.randn(10)})
a = df.a
expr_works = "log(a)/log(10)"
expr_notsupported = "log10(a)"
out_works = df.eval(expr_works)
out_notsupported = df.eval(expr_notsupported)
```
#### Problem description

As expected,   
```
    "\"{0}\" is not a supported function".format(name))
ValueError: "log10" is not a supported function
```
I know we can substitute the log10(a) behaviour with log(a)/log(10) but the pull request fix I'll post is a one word addition and makes things way more readable when you have long expressions

#### Expected Output

#### Output of ``pd.show_versions()``

<details>
[paste the output of ``pd.show_versions()`` here below this line]
pd.show_versions()
INSTALLED VERSIONS
------------------
commit: 5f46a28f918422b3199626becbaee561d22921c6
python: 3.6.7.final.0
python-bits: 64
OS: Linux
OS-release: 4.18.0-2-amd64
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8
pandas: 0.23.4
pytest: 4.0.1
pip: 10.0.1
setuptools: 39.1.0
Cython: 0.29.1
numpy: 1.15.4
scipy: 1.1.0
pyarrow: 0.11.1
xarray: 0.11.0
IPython: 7.2.0
sphinx: 1.8.2
patsy: 0.5.1
dateutil: 2.7.5
pytz: 2018.7
blosc: 1.6.2
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.8
feather: None
matplotlib: 3.0.2
openpyxl: 2.5.12
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.1.2
lxml: 4.2.5
bs4: 4.6.3
html5lib: 1.0.1
sqlalchemy: 1.2.14
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: 0.2.0
pandas_gbq: None
pandas_datareader: None
</details>
