gosrc.xml : use a more generic regexpr to match file/line numbers

This way liteide can also find the correct file when using testing libraries such as "github.com/stretchr/testify/assert".
For example it was not previously possible to open myfile_test.go with the folowing log in the console :

=== RUN TestAssertLib
--- FAIL: TestAssertLib (0.00 seconds)
	assertions.go:156:

	Location:	myfile_test.go:348

	Error:		test failure

FAIL
exit status 1
gosrc.xml : fix missing escape character in regexpr
gosrc.xml : remove leading \b in regexpr

with this change liteide can now successfully go to stack trace locations after a panic
(the first / character was excluded by \b)
Merge pull request #254 from vanackere/gosrc-regexpr

gosrc.xml : use a more generic regexpr to match file/line numbers