fix: call to crc32::Crc32c is ambiguous

[4kangjc]

When using C++17 to call the function crc32::Crc32c, and the parameter type is const char*, there is ambiguity.

[4kangjc]

$ cat test.cc
#include <string>

void f(std::string_view str) {}
void f(const std::string& str) {}

int main() {
  f("Hello World!");
}

$ g++ test.cc -std=c++17
test.cc:7:3: error: call to 'f' is ambiguous
  f("Hello World!");
  ^
test.cc:3:6: note: candidate function
void f(std::string_view str) {}
     ^
test.cc:4:6: note: candidate function
void f(const std::string& str) {}
     ^
1 error generated.

[4kangjc]

Hello, @pwnall.
Please review the code.