test: make max MP test stronger

As mentioned in #82, increasing `currentTime` by 1 second isn't enough
to actually create new MPs, so the test could return false positives.

This change increases the time between checks arbritraryly longer, such
that MPs would actually be created if the max MP wasn't reached.

Closes #82

test/RewardsStreamerMP.t.sol

@@ -790,7 +790,8 @@ contract StakeTest is RewardsStreamerMPTest {
 
         // move forward in time to check we're not producing more MP
         currentTime = vm.getBlockTimestamp();
-        vm.warp(currentTime + 1);
+        // increasing time by some big enough time such that MPs are actually generated
+        vm.warp(currentTime + 14 days);
 
         streamer.updateGlobalState();
         streamer.updateAccountMP(vaults[alice]);