Use getAbsolutePath instead of getCanonicalPath in executeProtoc.
Use getAbsolutePath instead of getCanonicalPath in executeProtoc.

Using getCanonicalPath in executeProtoc has adverse effect in less
standard environments, such as Bazel compilation sandbox -- since
the file is on a path with a symlinked directory, getCanonicalPath
rewrites the path to one outside the sandbox. All the -I arguments
were still inside sandbox, and thus protoc failed with:

``` File does not reside within any path specified using
--proto_path (or -I).  You must specify a --proto_path which
encompasses this file.  Note that the proto_path must be an exact
prefix of the .proto file names -- protoc is too dumb to figure
out when two paths (e.g. absolute and relative) are equivalent
(it's harder than you think). ```

Signed-off-by: Milan Plzik <565e34b63925dfd6e7d99b45792462d3cc4d81b7@ceai.io>

thesamet/sbt-protoc