package/ci: heh, attempted to install in /usr/local on iOS.

And on the new Macs it isn't writable by default anymore.

package/ci/ios-simulator-gles.sh

@@ -55,6 +55,7 @@ cmake .. \
     -DCMAKE_OSX_ARCHITECTURES="x86_64" \
     -DCMAKE_PREFIX_PATH="$HOME/deps" \
     -DCORRADE_RC_EXECUTABLE=$HOME/deps-native/bin/corrade-rc \
+    -DCMAKE_INSTALL_PREFIX=$HOME/deps \
     -DMAGNUM_TARGET_GLES2=$TARGET_GLES2 \
     -DMAGNUM_WITH_AUDIO=ON \
     -DMAGNUM_WITH_VK=OFF \