change target to x86_64 to keep answers consistent with spack 0.22 (#198)

Author: anton-seaice

spack.yaml

@@ -95,7 +95,7 @@ spack:
 
     all:
       prefer:
-      - 'target=x86_64_v4'
+      - 'target=x86_64'
   view: true
   concretizer:
     unify: true