fix script for preparing contracts package

(cherry picked from commit eaee98f2275f55b9749b11c6ae3e273a3eef2165)

contracts/package.json

@@ -4,7 +4,7 @@
   "description": "Secure Smart Contract library for Solidity",
   "files": [
     "**/*.sol",
-    "/build/*.json",
+    "/build/contracts/*.json",
     "!/mocks",
     "!/examples"
   ],

scripts/prepare-contracts-package.sh

@@ -9,4 +9,5 @@ if [[ ! -v ALREADY_COMPILED ]]; then
 fi
 
 cp README.md contracts/
-cp -Tr build/contracts contracts/build
+mkdir contracts/build contracts/build/contracts
+cp -r build/contracts/*.json contracts/build/contracts