Local currency issues - y axis and toggling to USD

## I'm submitting a ...
Check one of the following options with "x" and add the appropriate label to the issue as well

[x] Bug report 

[ ] Regression (behaviour that used to work and stopped working in a new release)

**Describe the Issue**
The local currency charts' y axes do not drop below zero, and then when you toggle back to USD, those charts suffer from the same issue.

**To Reproduce**
Replace the content below with the steps to reproduce the behaviour.
1. Go to a country profile
2. Click on the government finance charts
3. Toggle between local and USD
4. See error

**Expected Behaviour**
Both types of chart's y axes are scaled to below zero, where appropriate

**Screenshots/GIF**
Nigeria:

**Desktop (please complete the following information):**
- OS: Windows 7
- Browser: Chrome

**Environment/Server:**

- [ ] Production

- [x] Staging

- [ ] Test

- [ ] Development

**Additional Context**
Add any other context about the problem here.

Requested Delivery Date: 08/10/2018