Updated GLM 0.9.2.6 release note

readme.txt

@@ -41,6 +41,7 @@ GLM 0.9.2.6: 2011-10-01
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 - Fixed half based type build on old GCC
 - Fixed /W4 warnings on Visual C++
+- Fixed some missing l-value swizzle operators
 
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 GLM 0.9.2.5: 2011-09-20