ResNet18 import fixation

[sayakpaul]

Referring to the models_keras.py script, ResNet18 is being imported as from classification_models.keras import Classifiers but I was unable to find the classification_models module in the first place.

I swapped it with:

from keras.applications.resnet import ResNet18
model = ResNet18(
            weights='imagenet' if pretrained else None,
            input_tensor=input,
            include_top=False)