Correct error in the solution for subsetting data: exercises - exercise 1

[SvonGrebmer]

Inconsistency in the solution for Exercise 1:

Exercise 1:
Correct the following code, so only the first 10 rows and the last three columns are extracted:

characters[4:6, 10]

The solution provided here is characters[1:10, 4:6], but should be characters[1:10, 5:7]

[darakhshannehal]

PR opened to address this: #24