Apply modernize-use-nullptr.

test/boostTest.cpp

@@ -187,7 +187,7 @@ test_suite* init_unit_test_suite( int /*argc*/, char* /*argv*/[] )
 	if (solidity::test::CommonOptions::get().disableSMT)
 		removeTestSuite("SMTChecker");
 
-	return 0;
+	return nullptr;
 }
 
 // BOOST_TEST_DYN_LINK should be defined if user want to link against shared boost test library

tools/yulPhaser/SimulationRNG.cpp

@@ -52,5 +52,5 @@ uint32_t SimulationRNG::generateSeed()
 	// This is not a secure way to seed the generator but it's good enough for simulation purposes.
 	// The only thing that matters for us is that the sequence is different on each run and that
 	// it fits the expected distribution. It does not have to be 100% unpredictable.
-	return time(0);
+	return time(nullptr);
 }