Fix size_t error
Fix size_t error

Without this trivial change, I got the following error:
compiling SimpleString.cpp
cc1plus: warnings being treated as errors
src/CppUTest/SimpleString.cpp: In member function ‘void
SimpleString::split(const SimpleString&, SimpleStringCollection&)
const’:
src/CppUTest/SimpleString.cpp:153: error: conversion to ‘size_t’ from
‘int’ may change the sign of the result

bithium/cpputest,devMichaelJones/cpputest,chenlianbing/cpputest,asgeroverby/cpputest,bithium/cpputest,dawid-aurobit/cpputest,cpputest/cpputest,cpputest/cpputest,asgeroverby/cpputest,offa/cpputest,basvodde/cpputest,Andne/cpputest,jaeguly/cpputest,dawid-aurobit/cpputest,bithium/cpputest,offa/cpputest,asgeroverby/cpputest,chenlianbing/cpputest,dawid-aurobit/cpputest,chenlianbing/cpputest,PaulBussmann/cpputest,jaeguly/cpputest,arstrube/cpputest,dawid-aurobit/cpputest,PaulBussmann/cpputest,basvodde/cpputest,maxilai/cpputest,cpputest/cpputest,devMichaelJones/cpputest,jaeguly/cpputest,jaeguly/cpputest,maxilai/cpputest,Mindtribe/cpputest,devMichaelJones/cpputest,KisImre/cpputest,devMichaelJones/cpputest,arstrube/cpputest,cpputest/cpputest,basvodde/cpputest,maxilai/cpputest,asgeroverby/cpputest,Mindtribe/cpputest,bithium/cpputest,Mindtribe/cpputest,arstrube/cpputest,Andne/cpputest,offa/cpputest,Andne/cpputest,maxilai/cpputest,PaulBussmann/cpputest,Mindtribe/cpputest,arstrube/cpputest,chenlianbing/cpputest,KisImre/cpputest,KisImre/cpputest,Andne/cpputest,basvodde/cpputest,KisImre/cpputest,offa/cpputest,PaulBussmann/cpputest