Fix English grammar error (a misplaced modifier) in Bazel summary.
The adverb "only" is meant to limit what is rebuilt ("what is necessary")
and not what is done ("rebuild"), so it needs to be moved next to the
phrase it limits.
Build and test software of any size, quickly and reliably.
* **Speed up your builds and tests**:
- Bazel only rebuilds what is necessary.
+ Bazel rebuilds only what is necessary.
With advanced local and distributed caching, optimized dependency analysis and
parallel execution, you get fast and incremental builds.
