Specify UTF-8 encoding for all open() calls

docs/rules/periphery/periphery-split-csv.py

diff --git a/docs/rules/periphery/periphery-split-csv.py b/docs/rules/periphery/periphery-split-csv.py
index 904213d..e09ce59 100755
--- a/docs/rules/periphery/periphery-split-csv.py
+++ b/docs/rules/periphery/periphery-split-csv.py
@@ -240,7 +240,7 @@
 
 PERIPHERY_RULES_FILE = os.path.join('..', 'periphery-rules.rst')
 
-rst = open(PERIPHERY_RULES_FILE, 'w')
+rst = open(PERIPHERY_RULES_FILE, 'w', encoding='utf8')
 
 rst.write("""\
 .. Do **not** modify this file it is generated from the periphery.csv file
@@ -312,7 +312,7 @@
 
     rst.write('\n\n')
 
-    with open(rt.csv_fname, 'w', newline='') as f:
+    with open(rt.csv_fname, 'w', newline='', encoding='utf8') as f:
         w = csv.DictWriter(f, headers)
         w.writeheader()
         for r in rt.rules:
@@ -331,5 +331,5 @@
 
 rst.close()
 
-with open(PERIPHERY_RULES_FILE) as f:
+with open(PERIPHERY_RULES_FILE, encoding='utf8') as f:
     print(f.read())