replace exit() with sys.exit() (#590)

kindlecomicconverter/comic2ebook.py

@@ -1105,13 +1105,13 @@ def checkTools(source):
         process.communicate()
         if process.returncode != 0 and process.returncode != 7:
             print('ERROR: 7z is missing!')
-            exit(1)
+            sys.exit(1)
     if options.format == 'MOBI':
         kindleGenExitCode = Popen('kindlegen -locale en', stdout=PIPE, stderr=STDOUT, stdin=PIPE, shell=True)
         kindleGenExitCode.communicate()
         if kindleGenExitCode.returncode != 0:
             print('ERROR: KindleGen is missing!')
-            exit(1)
+            sys.exit(1)
 
 
 def checkPre(source):

kindlecomicconverter/shared.py

@@ -23,6 +23,7 @@ from hashlib import md5
 from html.parser import HTMLParser
 from distutils.version import StrictVersion
 from re import split
+import sys
 from traceback import format_tb
 
 
@@ -133,4 +134,4 @@ def dependencyCheck(level):
         missing.append('Pillow 5.2.0+')
     if len(missing) > 0:
         print('ERROR: ' + ', '.join(missing) + ' is not installed!')
-        exit(1)
+        sys.exit(1)