Fix build for macOS

On macOS, size_t is neither uint32_t nor uint64_t. So compilation fails
because no update method corresponds. This casts the result of vector::size
to uint32_t to fix this, just as was done for strings in updateString.

Bug: N/A
Test: N/A
Change-Id: Icfd0ce32db4f770bd1b0c5f164c4c87e846ae1d9
diff --git a/include/minikin/Hasher.h b/include/minikin/Hasher.h
index 4e20195..dcfdd0b 100644
--- a/include/minikin/Hasher.h
+++ b/include/minikin/Hasher.h
@@ -58,7 +58,8 @@
     }
 
     inline Hasher& update(const std::vector<FontFeature>& features) {
-        update(features.size());
+        uint32_t size = features.size();
+        update(size);
         for (const FontFeature& feature : features) {
             update(feature);
         }