Fix #1478: Typo in stem_exclusion property serialization

Author: gmarz

src/Nest/Domain/Analysis/Analyzers/LanguageAnalyzer.cs

@@ -26,7 +26,7 @@ public LanguageAnalyzer(Language language)
 		[JsonProperty("stopwords")]
 		public IEnumerable<string> StopWords { get; set; }
 
-		[JsonProperty("stem_exclusion ")]
+		[JsonProperty("stem_exclusion")]
 		public IEnumerable<string> StemExclusionList { get; set; }
 
 		/// <summary>