Changed linenoiseHistoryLoad/Save to take a const char* to avoid warning when passing a literal string.

Changed linenoiseHistoryLoad/Save to take a const char* to avoid warning when passing a literal string.

xcode 4 on OSX (clang) complains about calls to linenoiseHistorySave(".history") with the following warning:
warning: Deprecations: Conversion from string literal to 'char *' is deprecated

Adding these const specifiers fixes the issue.