Remove extra spaces from generated pkgconfig file

[SuperSodaSea]

Currently the .pc file generated by rule utils.install.pkgconfig_importfiles looks like this:

prefix=...
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: Test
Description: Test
Version: 0.1.0
Libs:  -L${libdir} -lTest
Cflags:  -I${includedir}

Notice that there are two spaces after Libs: and Cflags:. This PR changes them to one space after the colon instead of two.