amend typo in amortization (#34)

fixes vavr-io/vavr#2013

Author: ahlusar1989

src/docs/asciidoc/usage_guide.adoc

@@ -413,7 +413,7 @@ Stream.from(1).filter(i -> i % 2 == 0);
 Legend:
 
 * const — constant time
-* const^a^ — amotized constant time, few operations may take longer
+* const^a^ — amortized constant time, few operations may take longer
 * const^eff^ — effectively constant time, depending on assumptions like distribution of hash keys
 * const^lazy^ — lazy constant time, the operation is deferred
 * log — logarithmic time