Fix code example in Process::Status#exit_code docs (#15381)

(cherry picked from commit 2b544f1)

Co-authored-by: Billy.Zheng <vil963@gmail.com>

src/process/status.cr

@@ -245,7 +245,7 @@ class Process::Status
   # Raises `RuntimeError` if the status describes an abnormal exit.
   #
   # ```
-  # Process.run("true").exit_code                                # => 1
+  # Process.run("true").exit_code                                # => 0
   # Process.run("exit 123", shell: true).exit_code               # => 123
   # Process.new("sleep", ["10"]).tap(&.terminate).wait.exit_code # RuntimeError: Abnormal exit has no exit code
   # ```
@@ -258,7 +258,7 @@ class Process::Status
   # Returns `nil` if the status describes an abnormal exit.
   #
   # ```
-  # Process.run("true").exit_code?                                # => 1
+  # Process.run("true").exit_code?                                # => 0
   # Process.run("exit 123", shell: true).exit_code?               # => 123
   # Process.new("sleep", ["10"]).tap(&.terminate).wait.exit_code? # => nil
   # ```