clang-format: [JS] fix whitespace around "of" operator.

Summary:
Previously:
    import {of } from 'x';
    of (null);

Now:
    import {of} from 'x';
    of(null);

Reviewers: djasper

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D31698

llvm-svn: 299533