In this kata, you've to count lowercase letters in a given string and return the letter count in a hash with 'letter' as key and count as 'value'. The key must be 'symbol' instead of string in Ruby and 'char' instead of string in Crystal.
Example: 
```python
letter_count('arithmetics') #=> {"a": 1, "c": 1, "e": 1, "h": 1, "i": 2, "m": 1, "r": 1, "s": 1, "t": 2}
```
def letter_count(s):
    count = {}
    for c in s:
        count[c] = count.get(c, 0) + 1
    
    return count
def letter_count(s):
    count = {}
    for c in s:
        count[c] = count.get(c, 0) + 1
    
    return count