Update binaries' supported macOS

Change-Id: If51b0395b509c8e943688a9f00352b4ac5800369
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>

README.md

@@ -8,7 +8,7 @@ The standalone binary packages support the following platforms:
 
 * Windows 7 or later
 * (K)Ubuntu Linux 16.04 (64-bit) or later
-* macOS 10.8 or later
+* macOS 10.10 or later
 
 ## Compiling Qt Creator
 

doc/src/overview/creator-supported-platforms.qdoc

@@ -97,7 +97,7 @@
 
             \endlist
 
-        \li \macos 10.8 or later with the following:
+        \li \macos 10.10 or later with the following:
 
             \list