Run getPassword only in MAC to avoid "A problem occurred starting process 'command 'security'"

[emanuelb]

See how it was fixed in different project:
coreyphillips/moonshine@1f5c8f8

Compiling the app not on MACOSX will fail with error:
"A problem occurred starting process 'command 'security'"

workaround is to run:
sed -i 's/getPassword("android_keystore")/""/g' ./app/build.gradle;

The correct fix is like in above commit link:

import org.apache.tools.ant.taskdefs.condition.Os
def pass = ""
if(Os.isFamily(Os.FAMILY_MAC)) {
    pass = getPassword(currentUser, keyChainId);
}