Fixed typo.

src/Shader.cpp

@@ -100,8 +100,8 @@ GLuint Shader::compile() {
             case Type::Vertex:      err << "vertex";        break;
             case Type::Geometry:    err << "geometry";      break;
             case Type::Fragment:    err << "fragment";      break;
-            case Type::TesselationControl: err << "tesselation control"; break;
-            case Type::TesselationEvaluation: err << "tesselation evaluation"; break;
+            case Type::TessellationControl: err << "tessellation control"; break;
+            case Type::TessellationEvaluation: err << "tessellation evaluation"; break;
         }
 
         /* Show error log and delete shader */

src/Shader.h

@@ -43,18 +43,18 @@ class MAGNUM_EXPORT Shader {
             Vertex = GL_VERTEX_SHADER,      /**< Vertex shader */
 
             /**
-             * Tesselation control shader
+             * Tessellation control shader
              *
              * @requires_gl40 Extension @extension{ARB,tessellation_shader}
              */
-            TesselationControl = GL_TESS_CONTROL_SHADER,
+            TessellationControl = GL_TESS_CONTROL_SHADER,
 
             /**
-             * Tesselation evaluation shader
+             * Tessellation evaluation shader
              *
              * @requires_gl40 Extension @extension{ARB,tessellation_shader}
              */
-            TesselationEvaluation = GL_TESS_EVALUATION_SHADER,
+            TessellationEvaluation = GL_TESS_EVALUATION_SHADER,
 
             /**
              * Geometry shader