Update make test command in readme

Avoid "not run" test error due to test not being built:

    The following tests FAILED:
              1 - mptest (Not Run)
    Errors while running CTest

https://stackoverflow.com/questions/733475/cmake-ctest-make-test-doesnt-build-tests

Author: ryanofsky

README.md

@@ -43,7 +43,7 @@ mkdir build
 cd build
 cmake ..
 make
-make test
+make all test
 make install
 ```