build: Fix build with Python 3.5

Starting in Python 3.6, Python will convert bytes to strings inside
json.load, assuming UTF-8 if I understand correctly.  In Python 3.5,
you either need to do that yourself, or open the files as text instead
of binary.  So this opens all JSON files as text to fix Python 3.5
support.

Although Python 3.5 went EOL a couple months ago, it was very recent,
and Python 3.5 is still shipping in the Debian-based distro we are
using.  So probably others still have it, as well.

Closes shaka-project#3004

Change-Id: I0c829fa1af6a92bcf7f40c4ca41a76de278d3eb1

build/compiler.py

@@ -419,7 +419,7 @@ def __init__(self, config_path):
 
     # To avoid getting out of sync with the source files jsdoc actually reads,
     # parse the config file and locate all source files based on that.
-    with open(self.config_path, 'rb') as f:
+    with open(self.config_path, 'r') as f:
       config = json.load(f)
     for path in config['source']['include']:
       full_path = _get_source_path(path)

build/generateLocalizations.py

@@ -248,7 +248,7 @@ def main(args):
   combined_localizations = {}
   for locale in args.locales:
     path = os.path.join(args.source, locale + '.json')
-    with open(path, 'rb') as f:
+    with open(path, 'r') as f:
       combined_localizations[locale] = json.load(f)
 
   doc = GenerateLocalizations(combined_localizations, args.class_name)