[vagrantfile] Fix exponentiation type coercion issue

Vagrantfile

@@ -11,7 +11,7 @@ Vagrant.configure("2") do |config|
   if host =~ /darwin/
     cpus = `sysctl -n hw.ncpu`.to_i
     # sysctl returns Bytes and we need to convert to MB
-    mem = `sysctl -n hw.memsize`.to_f / 1024^2 * mem_ratio
+    mem = `sysctl -n hw.memsize`.to_i / (1024^2) * mem_ratio
   elsif host =~ /linux/
     cpus = `nproc`.to_i
     # meminfo shows KB and we need to convert to MB