Cleaned up tab/space formatting in Makefile.

Author: klaas

regression/Makefile

@@ -19,7 +19,7 @@ DIRS = cbmc \
        cbmc-cpp \
        goto-cc-goto-analyzer \
        systemc \
-			 contracts \
+       contracts \
        # Empty last line
 
 # Tests under goto-gcc cannot be run on Windows, so appveyor.yml unlinks