Clarify `_.merge` description. [ci skip]
Clarify `_.merge` description. [ci skip]

Mention behaviour difference between merging plain objects and objects with non-Object prototypes. As discussed in #1455.

huyinghuan/lodash,Droogans/lodash,xiwc/lodash,woldie/lodash,hafeez-syed/lodash,woldie/lodash,msmorgan/lodash,Xotic750/lodash,Xotic750/lodash,stewx/lodash,lekkas/lodash,jshanson7/lodash,tquetano-r7/lodash,beaugunderson/lodash,jshanson7/lodash,steelsojka/lodash,stewx/lodash,Droogans/lodash,prawnsalad/lodash,andersonaguiar/lodash,timruffles/lodash,mshoaibraja/lodash,boneskull/lodash,transGLUKator/lodash,jshanson7/lodash,stewx/lodash,benweet/lodash,tonyonodi/lodash,steelsojka/lodash,tquetano-r7/lodash,tejokumar/lodash,hafeez-syed/lodash,mshoaibraja/lodash,AneesMohammed/lodash,huyinghuan/lodash,reggi/lodash,reggi/lodash,zestia/lodash,boneskull/lodash,transGLUKator/lodash,beaugunderson/lodash,tejokumar/lodash,transGLUKator/lodash,tquetano-r7/lodash,prawnsalad/lodash,woldie/lodash,Xotic750/lodash,rlugojr/lodash,zestia/lodash,mshoaibraja/lodash,hafeez-syed/lodash,xiwc/lodash,timruffles/lodash,huyinghuan/lodash,reggi/lodash,enng0227/lodash,enng0227/lodash,AneesMohammed/lodash,tejokumar/lodash,zestia/lodash,rlugojr/lodash,andersonaguiar/lodash,lekkas/lodash,Droogans/lodash,timruffles/lodash,lekkas/lodash,andersonaguiar/lodash,prawnsalad/lodash,benweet/lodash,AneesMohammed/lodash,msmorgan/lodash,benweet/lodash,tonyonodi/lodash,xiwc/lodash,enng0227/lodash