Improve compatiblity with Clang.

This patch is related to Dune's FS#1457.
(reviewed by fetzer)


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@12788 2fb0f335-1f38-0410-981e-8018bf24f1b0

dumux/implicit/common/implicitassembler.hh

@@ -473,7 +473,7 @@ protected:
                 // negative change of the storage term of the last
                 // iteration of the last time step...)
                 residual_[i] = storageTerm_[i];
-                residual_[i] *= -1;
+                residual_[i] *= -1.0;
             }
 
             reuseMatrix_ = false;