Only download missing deps, not build

.travis.yml

@@ -12,7 +12,7 @@ install:
   - if ! go get code.google.com/p/go.tools/cmd/cover; then go get golang.org/x/tools/cmd/cover; fi
   - go get github.com/mattn/goveralls
   - go get -d github.com/obscuren/qml && cd $HOME/gopath/src/github.com/obscuren/qml && git checkout v1 && cd $TRAVIS_BUILD_DIR
-  - ETH_DEPS=$(go list -f '{{.Imports}} {{.TestImports}} {{.XTestImports}}' github.com/ethereum/go-ethereum/... | sed -e 's/\[//g' | sed -e 's/\]//g' | sed -e 's/C //g'); if [ "$ETH_DEPS" ]; then go get $ETH_DEPS; fi
+  - ETH_DEPS=$(go list -f '{{.Imports}} {{.TestImports}} {{.XTestImports}}' github.com/ethereum/go-ethereum/... | sed -e 's/\[//g' | sed -e 's/\]//g' | sed -e 's/C //g'); if [ "$ETH_DEPS" ]; then go get -d $ETH_DEPS; fi
 before_script:
   - gofmt -l -w .
   - goimports -l -w .