Fix translating linkReferences

[yann300]

No description provided.

[axic]

@yann300 what was this change for?

[yann300]

for making sure linkReference for old compilers are mapping of mapping instead of array (i guess to be compliant to standard JSON I/O)
https://github.com/ethereum/solc-js/pull/242/files#diff-dd1cfac53126f7abb38b82058b4312afR69

can't say if this is still needed though.

[axic]

Need to add a test case to verify this. So basically the test case would use findLinkReferences with an old style link reference (__LibraryName_____...) ?

[yann300]

So basically the test case would use findLinkReferences with an old style link reference (LibraryName___...)

right I believe so, and the output should be compliant with JSON standard.