Fix bug on log10 representation (#190)

Author: odashi

src/latexify/codegen/expression_rules.py

@@ -252,7 +252,7 @@ class FunctionRule:
     "fsum": FunctionRule(r"\sum", is_unary=True),
     "gamma": FunctionRule(r"\Gamma"),
     "log": FunctionRule(r"\log", is_unary=True),
-    "log10": FunctionRule(r"\log_10", is_unary=True),
+    "log10": FunctionRule(r"\log_{10}", is_unary=True),
     "log2": FunctionRule(r"\log_2", is_unary=True),
     "prod": FunctionRule(r"\prod", is_unary=True),
     "sec": FunctionRule(r"\sec", is_unary=True),