remove .txt suffix from shader source files
diff --git a/progs/glsl/toyball.c b/progs/glsl/toyball.c
index b870435..2daaedd 100644
--- a/progs/glsl/toyball.c
+++ b/progs/glsl/toyball.c
@@ -16,8 +16,8 @@
 #include "shaderutil.h"
 
 
-static char *FragProgFile = "CH11-toyball.frag.txt";
-static char *VertProgFile = "CH11-toyball.vert.txt";
+static char *FragProgFile = "CH11-toyball.frag";
+static char *VertProgFile = "CH11-toyball.vert";
 
 /* program/shader objects */
 static GLuint fragShader;