ggplot functions are not working with ale and pdp plots for all features

I am trying to use `ggplot` functions with the `plot` function of `iml` package. But the additional aurgments are applied to only the last plot. Here is an example
```
#Load required packahes
library("iml")
library("randomForest")

# Train a random forest on the Boston dataset:
data("Boston", package = "MASS")
set.seed(42)
rf <- randomForest(medv ~ ., data = Boston, ntree = 50)

#create a Predictor object, that holds the model and the data
X <- Boston[which(names(Boston) != "medv")]
predictor <- Predictor$new(rf, data = X, y = Boston$medv)

# Compute the accumulated local effects for all features
ale <- FeatureEffects$new(predictor, method = "ale")

plot(ale) + theme_bw() +
theme(panel.grid.major = element_blank(),
panel.grid.minor = element_blank())+
theme(text=element_text(family = "serif", size=15),
axis.title.x = element_text(size = 18),
axis.title.y = element_text(size = 18),
axis.text.x = element_text(colour="black",face="bold"),
axis.text.y = element_text(colour="black",face="bold"))
```

Similarly for `pdp` plot also
```
# Compute the partial dependence plot for all features
pdp <- FeatureEffects$new(predictor, method = "pdp")
pdp$plot() + theme_bw() +
theme(panel.grid.major = element_blank(),
panel.grid.minor = element_blank())+
theme(text=element_text(family = "serif", size=15),
axis.title.x = element_text(size = 18),
axis.title.y = element_text(size = 18),
axis.text.x = element_text(colour="black",face="bold"),
axis.text.y = element_text(colour="black",face="bold"))
```

Now I have done some tweaking after getting the results inside the `ale` or `pdp` object and afterthat all the `ggplot` functions are working like
```
#PDP plotting
df2 <- pdp$results %>%
imap_dfr(., ~ data.frame(name = .y, Borders = .x$.borders, Value = .x$.value))

df2 %>%
ggplot(aes(x = Borders, y = Value)) +
geom_line(aes(group = name)) +
facet_wrap(name~., scales = "free") + theme_bw() +
theme(panel.grid.major = element_blank(),
panel.grid.minor = element_blank())+
theme(text=element_text(family = "serif", size=15),
axis.title.x = element_text(size = 18),
axis.title.y = element_text(size = 18),
axis.text.x = element_text(colour="black",face="bold"),
axis.text.y = element_text(colour="black",face="bold"))
```

```
#ALE plotting
df3 <- ale$results %>%
imap_dfr(., ~ data.frame(name = .y, Borders = .x$.borders, value = .x$.value))

df3 %>%
ggplot(aes(x = Borders, y = value)) +
geom_line(aes(group = name)) +
facet_wrap(name~., scales = "free") + theme_bw() +
theme(panel.grid.major = element_blank(),
panel.grid.minor = element_blank()) +
theme(text=element_text(family = "serif", size=15),
axis.title.x = element_text(size = 18),
axis.title.y = element_text(size = 18),
axis.text.x = element_text(colour="black",face="bold"),
axis.text.y = element_text(colour="black",face="bold"))
```

Can you can changes in the source code so that `ggplot` functions like `facet_wrap`, `theme` works for all the panels?