Fix the link of the gensymbol script from OpenBLAS

Author: amontoison

ext/gensymbol/README.md

@@ -1,4 +1,4 @@
 # gensymbol
 
-This uses [the `gensymbol` script from OpenBLAS](https://github.com/xianyi/OpenBLAS/blob/develop/exports/gensymbol) to generate a list of BLAS/LAPACK symbols from first principles.
+This uses [the `gensymbol` script from OpenBLAS](https://github.com/xianyi/OpenBLAS/blob/develop/exports/gensymbol.pl) to generate a list of BLAS/LAPACK symbols from first principles.
 To use this, run `./generate_func_list.sh` and it will automatically populate [the `src/exported_funcs.inc` file](../../src/exported_funcs.inc).