tool.sh: Suggest using '&&' instead of ';'

Running `make` when the `cmake .` prior to it failed will yield a
Captn-Obvious error, so suggest the user to only call `make` when
`cmake` succeeded.

tool.sh

@@ -10,7 +10,7 @@ SOURCE_FILE="$BASE/src/bindgen.cr"
 function print_clang_error {
   echo "  Bindgen requires a full installation of Clang, its libraries and development"
   echo "  headers.  Please install these first, and restart this script."
-  echo "  You can also manually run 'cmake .; make -j' in clang/ for debugging this issue."
+  echo "  You can also manually run 'cmake . && make -j' in clang/ for debugging this issue."
   echo "  Full path to clang/: $CLANG_DIR"
 
   exit 1