Datetime picker glitch in Safari

### I'm Submitting a ...

```
[x] Bug report
[ ] Feature request
[ ] Support request
```

### Steps to Reproduce

1. Install/run react-datetime demo
2. In Safari, click on Datetime input under 'Customization props' heading.

### Actual Results

If clicking in whitespace area of input, picker appears as intended. If clicking on text inside input, picker appears but then immediately hides.

This issue appears to be specific to Safari. Works as intended in Firefox. Unknown if specific to Safari version noted below.

### Other Information (e.g. stacktraces, related issues, suggestions how to fix)

Safari version 11.0
MacOS 10.12.6
react-datetime 2.10.2

Run the react-datetime demo and reproduce the problem in Safari 11.0 by clicking text and whitespace in the Datetime input under “Customization props”; compare the behavior with Firefox. Done means clicking either area opens the picker and it remains visible, without changing the reported behavior in Firefox.

Written by the indexing model from the issue text.