Exporting small decimals produces invalid JSON

When small decimal numbers are exported to JSON, the export uses exponential notation but gets the format wrong.

The following ink...

```
VAR epsilon = 0.000001
```
...exports to...
```
{"inkVersion":17,"root":["done",{"global decl":["ev",1E-06.0,{"VAR=":"epsilon"},"/ev","end",null],"#f":3}],"listDefs":{}}
```
...which is not valid JSON. Should be *1E-06*, not *1E-06.0*.

Reproduce the issue by exporting the shown VAR epsilon = 0.000001 example and inspect the JSON export path; the issue names no file or test. Done means the exported value uses 1E-06 rather than 1E-06.0 and the result is valid JSON.

Written by the indexing model from the issue text.