Pandas not available for Python 3.4
Hi just wanna asked why pandas 0.23.4 is not available for Python 3.4.
End of life is still months away (https://devguide.python.org/#status-of-python-branches)

#### Code Sample, a copy-pastable example if possible

None - This is a build issue from Travis CI

#### Problem description

It seems that pandas 0.23.4 is not available for Python 3.4

```
Collecting pandas==0.23.4 (from -r requirements.txt (line 3))
  Could not find a version that satisfies the requirement pandas==0.23.4 (from -r requirements.txt (line 3)) (from versions: 0.1, 0.2b0, 0.2b1, 0.2, 0.3.0b0, 0.3.0b2, 0.3.0, 0.4.0, 0.4.1, 0.4.2, 0.4.3, 0.5.0, 0.6.0, 0.6.1, 0.7.0rc1, 0.7.0, 0.7.1, 0.7.2, 0.7.3, 0.8.0rc1, 0.8.0rc2, 0.8.0, 0.8.1, 0.9.0, 0.9.1, 0.10.0, 0.10.1, 0.11.0, 0.12.0, 0.13.0, 0.13.1, 0.14.0, 0.14.1, 0.15.0, 0.15.1, 0.15.2, 0.16.0, 0.16.1, 0.16.2, 0.17.0, 0.17.1, 0.18.0, 0.18.1, 0.19.0rc1, 0.19.0, 0.19.1, 0.19.2, 0.20.0rc1, 0.20.0, 0.20.1, 0.20.2, 0.20.3, 0.21.0rc1, 0.21.0, 0.21.1, 0.22.0)
No matching distribution found for pandas==0.23.4 (from -r requirements.txt (line 3))
```
