Bugfix: Text Input problem type expects numeric answer when correct answer starts with a number

Description

Example:

```
>>Question.<<

= 100 test
or=test 100

```

Because the correct answer option (= 100 test) is a string that begins with the number, edX is treating the problem as though it requires a number answer, rather than a text string that can include letters and numbers. If the user enters an answer with text instead of just numbers, an error message that says "Error, couldn't parse formula" appears.

<img width="1177" alt="screenshot 2018-12-26 18 41 51" src="https://user-images.githubusercontent.com/1876893/50450321-37c83200-093e-11e9-8b3a-d6641a865963.png">

<img width="948" alt="screenshot 2018-12-26 18 42 01" src="https://user-images.githubusercontent.com/1876893/50450322-37c83200-093e-11e9-9df5-1d1036af7267.png">

Assignee

Simon Chen

Reporter

Open Source Pull Request Bot

Contributor Name

Dmitry Viskov

Repo

edx/edx-platform

Customer

Epic Link

None

OSCM Assignee

None

Platform Map Area (Levels 1 &amp; 2)

None

Platform Map Area (Levels 3 &amp; 4)

None

Blended Hour Utilization Percentage

None

Priority

Unset
Configure