Disable SIMD for stb_image, closes #5

src/deps/stb/stb.cpp

 
 #define STB_IMAGE_IMPLEMENTATION
 #define STBI_ASSERT(x) assert(x)
+#define STBI_NO_SIMD
 #include "stb/stb_image.h"
 
 #define STB_IMAGE_WRITE_IMPLEMENTATION