docs/GL3.txt: fix typo
docs/GL3.txt: fix typo

Signed-off-by: Boyan Ding <78666b9fbf8dff57999b5e685e13976b1e2e71e0@gmail.com>
Reviewed-by: Albert Freeman <fdca1a49fd7b3c72c5ac316d88a493530c6c6a02@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler