Auto merge of #3253 - nipunn1313:exe, r=alexcrichton

Add an [EXE] hamcrest substitution for file extension

This should make the testing a bit more precise as to whether
we expect targets of the form foo.exe vs foo-abc123.exe. I
was also considering adding a [/] substitution for the fwd
slash vs backslash [..], but thought I would leave that to another PR
if we thought that was a good idea.