add custom make clean rule for dynet_scala jar
add custom make clean rule for dynet_scala jar


Former-commit-id: ff090f82f5c4c765dca04a8b4e2086fea15964da
clab/dynet,shuheik/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,clab/cnn,chunyang-wen/dynet,xunzhang/dynet,danielhers/dynet,shuheik/dynet,xunzhang/dynet,clab/dynet,xunzhang/dynet,shuheik/dynet,danielhers/dynet,danielhers/dynet,clab/cnn,shuheik/dynet,clab/dynet,xunzhang/dynet,clab/dynet,shuheik/dynet,chunyang-wen/dynet,clab/dynet,chunyang-wen/dynet,shuheik/dynet,clab/cnn,danielhers/dynet,danielhers/dynet,chunyang-wen/dynet,danielhers/dynet,clab/dynet