MNEMONIC-512: Upgrade Apache parent POM to version 21
MNEMONIC-512: Upgrade Apache parent POM to version 21

NonVolatileComputing/incubator-mnemonic,NonVolatileComputing/incubator-mnemonic,yzz127/incubator-mnemonic,yzz127/incubator-mnemonic,lql5083psu/incubator-mnemonic,lql5083psu/incubator-mnemonic,yzz127/incubator-mnemonic,lql5083psu/incubator-mnemonic,yzz127/incubator-mnemonic,NonVolatileComputing/incubator-mnemonic,NonVolatileComputing/incubator-mnemonic,lql5083psu/incubator-mnemonic