Update versions of conan dependencies

Author: piponazo

conanfile.py

@@ -21,7 +21,7 @@ def configure(self):
         self.options['gtest'].shared = False
 
     def requirements(self):
-        self.requires('zlib/1.2.11')
+        self.requires('zlib/1.2.12')
 
         if self.options.webready:
             self.requires('libcurl/7.79.0')
@@ -37,7 +37,7 @@ def requirements(self):
         if self.options.xmp:
             self.requires('XmpSdk/2016.7@piponazo/stable') # from conan-piponazo
         else:
-            self.requires('expat/2.4.1')
+            self.requires('expat/2.4.8')
 
     def imports(self):
         self.copy('*.dll', dst='bin', src='bin')