Removed "<:" bigram confusing gcc 4.4

Resulted in error:

```test/cpp/end2end/end2end_test.cc:120: error: ‘<::’ cannot begin a template-argument list
test/cpp/end2end/end2end_test.cc:120: note: ‘<:’ is an alternate spelling for ‘[’. Insert whitespace between ‘<’ and ‘::’
test/cpp/end2end/end2end_test.cc:120: note: (if you use ‘-fpermissive’ G++ will accept your code)
make: *** [objs/opt/test/cpp/end2end/end2end_test.o] Error 1```