gcc8.2 unsigned int to unsigned char conversion warning

[furkanusta]

gcc 8.2 & cmake 3.12

Compiler output:

In file included from ../src/lib_json/../../include/json/writer.h:10,
from ../src/lib_json/json_writer.cpp:8:
../src/lib_json/../../include/json/value.h: In member function ‘void Json::Value::setType(Json::ValueType)’:
../src/lib_json/../../include/json/value.h:615:51: warning: conversion from ‘unsigned int’ to ‘unsigned char’ may change value [-Wconversion]
void setType(ValueType v) { bits_.value_type_ = v; }