Update src/fpm_environment.f90

Co-authored-by: Sebastian Ehlert <28669218+awvwgk@users.noreply.github.com>

Author: urbanjost

src/fpm_environment.f90

@@ -158,7 +158,7 @@ subroutine run(cmd,echo,exitstat)
         else
             if (stat /= 0) then
                 print *, 'Command failed'
-                stop 
+                stop 1
             end if
         end if