Insist on Tesseract 3.04 wherever we check for it

ocrmypdf/__main__.py

@@ -39,7 +39,7 @@ warnings.simplefilter('ignore', pypdf.utils.PdfReadWarning)
 # -------------
 # External dependencies
 
-MINIMUM_TESS_VERSION = '3.02.02'
+MINIMUM_TESS_VERSION = '3.04'
 
 
 def complain(message):

setup.py

@@ -155,7 +155,7 @@ if not forced and command.startswith('install') or \
         command in ['check', 'test', 'nosetests', 'easy_install']:
     check_external_program(
         program='tesseract',
-        need_version='3.03',  # limited by Travis CI / Ubuntu 14.04 backports
+        need_version='3.04',  # using backport for Travis CI
         package={'darwin': 'tesseract', 'linux': 'tesseract-ocr'}
     )
     check_external_program(