Issue with stop statement

Hi, 
I came across the following bug in fprettify. While parsing a line containing a stop statement such as:
```
if (condition) stop 'A message'
```
fprettify removed the space between stop and 'A message'. I.e.
```
if (condition) stop'A message'
```
This then results in a compilation error when compiling with gfortran.
Hope this helps!
Ben
