[System.ServiceModel.Web] Fix tarball generated by "make dist"

System.Runtime.Serialization.Json/JavaScriptReader.cs is needed by the System.Json assembly, but in
d44898a2308b06a1b51b646e519da1ac3daaf6b4 it was removed from net_2_0_System.ServiceModel.Web.dll.sources
which means it wasn't included in the tarball anymore and building it failed.

Fixing the tarball by including the file in EXTRA_DISTFILES.

mcs/class/System.ServiceModel.Web/Makefile

@@ -27,7 +27,8 @@ TEST_MCS_FLAGS = $(LIB_MCS_FLAGS)
 EXTRA_DISTFILES = $(RESOURCE_FILES) \
 	Test/config/webHttpBinding \
 	Test/config/webHttpBinding.config \
-	System.Runtime.Serialization.Json/DataContractJsonSerializerSettings.cs
+	System.Runtime.Serialization.Json/DataContractJsonSerializerSettings.cs \
+	System.Runtime.Serialization.Json/JavaScriptReader.cs
 
 VALID_PROFILE := $(filter 2 4, $(FRAMEWORK_VERSION_MAJOR))
 ifndef VALID_PROFILE