update cmake opts in README.build

via "DevYourWorld" on github

https://github.com/warmcat/libwebsockets/issues/64



Signed-off-by: Andy Green <andy.green@linaro.org>

README.build

@@ -98,9 +98,9 @@ To list avaialable options (ommit the H if you don't want the help text):
 
 Then to set an option and build (for example turn off SSL support):
 
-	cmake -DWITH_SSL=0 ..
+	cmake -DLWS_WITH_SSL=0 ..
 or
-	cmake -DWITH_SSL:BOOL=OFF ..
+	cmake -DLWS_WITH_SSL:BOOL=OFF ..
 
 Unix GUI
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