Update shader_basic_pbr example to work on web

changed to GLSL_VERSION            100
update glsl100 shader
set float  precision  to highp
removed keyword  in
change for loop tu use constant value  gives an error

examples/shaders/shaders_basic_pbr.c

@@ -22,7 +22,7 @@
 #if defined(PLATFORM_DESKTOP)
     #define GLSL_VERSION            330
 #else   // PLATFORM_ANDROID, PLATFORM_WEB
-    #define GLSL_VERSION            120
+    #define GLSL_VERSION            100
 #endif
 
 #include <stdlib.h>             // Required for: NULL