Add tr transformations for text exercises

- script-01.sh: replace all '!' with '.' using tr.
- script-02.sh: swap Y and Z (both upper and lower case) using tr.

Author: Iswanna

shell-pipelines/tr/script-01.sh

@@ -6,3 +6,5 @@ set -euo pipefail
 # The author got feedback that they're using too many exclamation marks (!).
 #
 # TODO: Write a command to output the contents of text.txt with every exclamation mark (!) replaced with a full-stop (.).
+
+tr '!' '.' < ./text.txt

shell-pipelines/tr/script-02.sh

@@ -7,3 +7,5 @@ set -euo pipefail
 # so every Y should be a Z, and every Z should be a Y!
 #
 # TODO: Write a command to output the contents of text.txt with every Y and Z swapped (both upper and lower case).
+
+tr 'YZyz' 'ZYzy' < ./text.txt