Changed license field to BSD-3-Clause.
Changed license field to BSD-3-Clause.

npm v2.15.8, and presumably all newer versions, report that the license field is
"not a valid SPDX license". I changed the license field in package.json to the
correct key which matches the LICENSE file against https://spdx.org/licenses/.

looker/tracing-framework,google/tracing-framework,google/tracing-framework,google/tracing-framework,looker/tracing-framework,looker/tracing-framework,google/tracing-framework,looker/tracing-framework