[buildifier] Proper handling of scientific notation in arguments

[jakeBass]

Currently,

tolerance = 5e-3

gets formatted to

tolerance = 5e - 3

as if the numbers were being subtracted. This is less clear than keeping the characters all adjacent to each other.

To reproduce the issue, clone the repo. Then run:

$ echo 'filegroup(name="foo", tolerance = 5e-3)' > BUILD.bazel
$ cat BUILD.bazel
filegroup(name="foo", tolerance = 5e-3)
$ buildifier BUILD.bazel
$ cat BUILD.bazel
filegroup(
    name = "foo",
    tolerance = 5e - 3,
)