Cherry-pick fixes for latest dqrng release.

The recent dqrng 0.4.0 release has a few small incompatible changes that
makes the build fail.

The changes necessary have been applied to the dev branch already as
part of larger pull requests #280 and #305. This commit cherry-picks
just the fixes for the master branch.

src/Random.cpp

@@ -60,8 +60,8 @@ void Random::prop_sample_bucket(
 
     // all probabilities are the same
     if (heavy == n) {
-        for (auto i = 0; i < size; ++i) {
-            *result = (*rng)(n);
+        for (size_t i = 0; i < size; ++i) {
+            *result = (*rng)((uint64_t)n);
             ++result;
         }
         return;
@@ -121,9 +121,9 @@ void Random::prop_sample_bucket(
     }
 
     // sample
-    for (auto i = 0; i < size; ++i) {
-        size_t bucket = (*rng)(n);
-        double acceptance = dqrng::uniform01((*rng)());
+    for (size_t i = 0; i < size; ++i) {
+        size_t bucket = (*rng)((uint64_t)n);
+        double acceptance = rng->uniform01();
         *result = (acceptance < dividing_probs[bucket]) ? bucket :
             alternative_index[bucket];
         ++result;