use consistent label on code fence

Code fences of Fortran now carry a uniform label.

Signed-off-by: Norwid Behrnd <[email protected]>

Author: nbehrnd

README.md

@@ -43,7 +43,7 @@ Compare `examples/*before.f90` (original Fortran files) with
 `examples/*after.f90` (reformatted Fortran files) to see what fprettify does. A
 quick demonstration:
 
-```Fortran
+```fortran
 program demo
 integer :: endif,if,elseif
 integer,DIMENSION(2) :: function
@@ -61,7 +61,7 @@ end program
 
 ⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩ `fprettify` ⇩⇩⇩⇩⇩⇩⇩⇩⇩⇩
 
-```Fortran
+```fortran
 program demo
    integer :: endif, if, elseif
    integer, DIMENSION(2) :: function